PART III. PROCESSES OF REPRODUCING ILLUSTRATIONS.

METHODS EMPLOYED.

The preliminary work in producing illustrations includes the preparation, from originals submitted by authors, of drawings and other kinds of "copy" in such a way that the copy can be reproduced in multiple by printing.

Several processes are used for preparing plates for printing illustrations, and each has its peculiar features of excellence. One process may render fine details with facility but may fail in uniformity in large editions; another may be cheap and effective on the whole but may not reproduce fine details; and still another may give fine color or tone effects but may be too expensive. Therefore a knowledge of the varied uses and results and of the cost of the several processes of reproduction and, on the other hand, of the kinds of originals that are best suited for reproduction by any one of the processes is essential to effectiveness and economy in planning, preparing, and reproducing an illustration.

The following condensed descriptions of processes are intended mainly to aid in determining the kind of copy that is appropriate for each process and the kind and quality of reproduction to be expected, so that only the principal operations or stages in each process are described. Wood engraving, which was used in making printing plates for many of the illustrations in the early publications of the Geological Survey, is described here only to compare that laborious and "indirect" method of engraving cuts with the more modern kinds of relief engraving. In 1892 it gave way to photo-engraving.

PHOTO-ENGRAVING.

GENERAL FEATURES

The term "photo-engraving" is applied to processes by which a black and white line drawing, photograph, or like original is reproduced in relief on a metal plate from which prints may be made on an ordinary printing press, in distinction from processes that print from flat or relatively flat surfaces, such as the lithographic and photogelatin processes. The photo-engraving processes that are most generally used are those called "zinc etching" and "half-tone engraving." These processes depend on the discovery that gelatin or similar organic material, if treated with potassium or ammonium bichromate and exposed to the action of light, is made insoluble in water. If a metal plate coated with bichromatized gelatin or albumen is exposed to light under a negative the parts acted upon by light become insoluble and those not acted upon remain unchanged and may be washed away so as to expose the metal, which is then etched with acid in order to give relief to the unexposed parts and make of them a printing surface.

ZINC ETCHING.

Zinc etching is adapted to the direct reproduction of a pen and ink drawing composed of lines, dots, or solid black areas. On the finished metal plate these lines, dots, and solid areas form the printing surface, and the spaces between them, which have been etched away, represent the white or blank parts of the picture. The process is cheap and is almost universally used for reproducing small drawings designed for text illustrations. It is also well adapted to the reproduction of maps and diagrams measuring in print not more than about 10 by 14 inches. One of the chief advantages of this and of all other direct (photographic) processes of engraving is that they reproduce a drawing in facsimile, whereas the "personal equation" must enter into all engravings made by an indirect method--that is, by hand--such as wood engraving, wax engraving, and engraving on stone or copper, which make it necessary to compare every detail of the proof with every detail of the drawing before the engraving can be approved. The pen drawing to be reproduced, which should preferably be considerably larger than the completed engraving, is first photographed to the proper size or scale on an ordinary negative film. The film is then stripped from the negative and reversed in order that the etched plate may print the design as in the original and that the film may be grouped with other films on one large glass and all printed at the same time. The negative (whether a single film or several) is then placed in a specially constructed printing frame in contact under pressure with a sensitized zinc plate and exposed to light.

After the zinc plate has been removed from the printing frame (in the dark room) the plate is rolled with printer's transfer ink, which resists acid, and placed in a shallow tray containing water, in which it is rocked for several minutes, and then taken out and rubbed gently with cotton. The parts of the coating of the plate that were acted on by light have become insoluble and will therefore be unaffected by the water, but the parts of the coating not acted on by light and therefore not hardened will be removed by the washing, which will expose the metal and leave the parts acted on by light--the picture--in black lines, dots, etc. The plate is then dusted with "topping powder," a resinous substance which adheres only to the parts carrying the ink. The plate is then heated so that the resin and the ink that remain fuse together and form, when cooled, a resistant surface which will not be affected by the acid to be used later in etching the unprotected parts of the plate.

The plate is now ready for a preliminary etching in a fluid consisting of water and a few drops of nitric acid. It is placed in a tray, rocked gently for a short time, and then removed, washed well in running water, drained, and dried with gentle heat. "Dragon's blood," a resinous powder that resists the action of acid, is next applied to the plate, in order to protect the sides of the lines and the dots from the acid, and the plate is then heated just sufficiently to melt the powder and units it with the ink. A small quantity of nitric acid is now added to the etching bath, and the plate is subjected to its first thorough biting or etching. It is then removed from the bath, washed under a tap, carefully wiped with a damp rag, and dried with gentle heat.

The plate is thus treated three or more times until it is etched deep enough to insure satisfactory printing, and it is then ready for finishing, which consists of deepening the larger open spaces between the lines with a routing machine and of cutting away with hand gravers lines that are improperly connected or that are so close together that they will not print separately. The routing machine is provided with a cutting tool mounted on a revolving spindle that projects downward into the engraved plate, which is securely fastened. The movement of the arm that holds the cutter is universal and can be controlled with great precision. The plate is then "proved" that is, a proof is taken from it on paper and if the proof is satisfactory the plate is nailed to a block of wood on which it will be "type high" (0.918 inch), for printing.

Most drawings for zinc etching are made with a pen in black ink and consist of lines, dots, or masses of black, but drawings may also be prepared by using some medium that will produce a fine stipple, such as a black crayon on rough paper or Ross's stipple paper. (See p. 24.) The drawing should be one and one-half to two or three times as large as the printed illustration, for it is impossible to obtain a satisfactory reproduction of a pen and ink drawing without some reduction. If the drawing has not been reduced the lines appear heavier in the reproduction than in the drawing, and imperfections thus become more noticeable; if it has been properly reduced, imperfections are diminished and the lines and dots become thinner and finer than those in the drawing. In making a drawing that is to be reduced the draftsman can also space his lines farther apart and work out his details more easily.

An author should carefully examine and approve the finished drawings, which can, of course, be greatly altered, if necessary, before they are engraved; but similar corrections can not be made on proof sheets of zinc cuts, which should not be marked for alterations except by eliminating parts. Minor changes can be made in such a cut by an expert "finisher," but if the cut is small it is generally cheaper to correct the drawing and have a new cut made.

Zinc etchings cost about 10 to 25 cents a square inch, the cost being varied according to a standard scale which is based upon the ascertained cost of reproduction. The minimum charge for a single cut is $2.

COPPER ETCHING IN RELIEF.

Copper etching, which produces a line cut in relief, requires the same kind of copy that is most often marked for zinc etching and is used to obtain deeper etching and a more permanent cut. It is said to produce better printing plates than those etched on zinc and is used largely for reproducing script lettering and other fine work. As copper plates will hold up longer in printing than zinc, a cut etched on copper may not need to be electrotyped.

The chemical part of the process is practically the same as that employed for etching half-tone plates, described under the next heading.

The cost of etching on copper is considerably greater than the cost of etching on zinc. This process is not often used in reproducing illustrations for publications of the Geological Survey.

HALF-TONE ENGRAVING.

The half-tone process is, in name at least, familiar to almost everyone who has had any connection with the making of books, whether as author, editor, illustrator, or printer. The invention of a photomechanical process of reproducing a line drawing to make a metal plate that could be printed along with type on an ordinary printing press naturally led to attempts to reproduce similarly a photograph. It was known that the intermediate shades between white and black in a photograph--the half tones--can be reproduced on an ordinary printing press only by breaking them up into dots or lines that will form a good printing surface and that by their variation in size or density will give for each shade the effect of a uniform tone. In the half-tone process this effect is produced by photographing the picture or object through a screen.

The half-tone screen consists of two plates of glass, on each of which lines running generally at an angle of 45° to the sides of the plate have been engraved, cemented together so that the lines cross at right angles. The lines, which are minute grooves filled with an opaque black pigment, thus appear as a series of black crossed lines on a white ground. The screen is placed in the camera in front of the negative. Screens are made that show from 60 lines to an inch for the coarser newspaper illustrations to 250 lines or more to the inch for fine book work. The screens used for magazine illustrations generally show 120 to 150 lines. Those used for Survey publications show 150 to 175 lines, and for reproducing delicate drawings and photographs of fossils screens bearing 200 lines to the inch are sometimes specified; but these finer screens require the use of highly super-coated papers, some of them made of cheap fiber and not known to be permanent. For a half tone that is to be printed in the text a 100-line or a 120-line screen is specified. (See Pl. VI, p. 56.)

The method of etching a half-tone plate does not differ greatly from that used in zinc etching, and there are several kinds of half-tone plates, though most of them are etched on copper, not on zinc, those etched on zinc being used principally for newspaper illustrations. The half-tone screen is used also in other processes to obtain a negative.

When a half-tone negative hag been made the film is stripped from the glass plate and reversed, as in the zinc-etching process, though some half-tone engravers use a mirror box or prism by which the picture is so disposed on the negative that it does not need stripping and reversing. A perfectly flat, clean, and highly polished copper plate, generally large enough to accommodate several such films, is then coated with a sensitive film according to one of several formulas, all based on the fact that gelatin or some similar body, if sensitized with certain chromic salts, becomes hardened and insoluble in water on exposure to light. This plate is then placed in the printing frame in contact, under pressure, with the glass negative plate and is exposed to light in the usual manner. The copper plate is then removed from the frame in the dark room and made ready for etching.

For etching half-tone plates on copper a saturated solution of perchloride of iron is used instead of the solution of nitric acid used for zinc etching. The time of etching ranges from about 5 to 15 minutes, according to the strength of the solution. One etching is generally sufficient, but it may be necessary to give the plate another "biting" if it has not been etched deep enough, or to re-etch it in order to strengthen contrasts. If, for instance, the sky in a half-tone plate shows too dark or is uneven in tint it can be made lighter or more even by re-etching. On the other hand, if certain features on a plate are too light they can be darkened by burnishing--rubbing the surface with a highly polished steel burnisher under just sufficient pressure to flatten slightly the fine points that form the printing surface of the plate. When the plate leaves the hands of the etcher it is turned over to the finisher, who with a graver removes spots or any other imperfections that may appear on it. Sometimes a roulette is used to lighten parts, and other tools are used for special purposes.

After a plate that shows two or more pictures has been etched and finished it is divided by sawing them apart. Each one is then put into a beveling machine, where its edges are trimmed and the usual border is made, if it is desired. The separate plates are then ready to be proved and mounted on blocks of wood which make them type high, ready for printing.

The half-tone process is used almost exclusively for reproducing photographs and wash drawings, though it will produce a facsimile of any kind of copy, such as impressions from type, old manuscripts, or typewriting, but a shade composed of minute black dots will appear over the entire print and there will be no absolutely whits areas unless they are produced by routing the plate or cutting out the high lights. (See p. 74.) The reproduction of an ordinary outdoor photograph requires very little handwork, except for re-etching, burnishing, and cutting the borders. In the reproduction of copy that is made up of separate parts, such as groups of photographs of specimens that are to appear on a white ground, the half-tone "tint"--or more properly shade--between and around the several figures must be removed and numbers must be added. This operation requires two negatives--one half tone and one line--and produces what is called a "combination" plate. Therefore the difference in the cost of making a half-tone cut from a single photograph of a landscape and from a cut made from "copy" of the same size consisting of a number of small photographs or drawings, to which numbers or letters are added, is considerable (about 50 per cent greater) and depends upon the amount of additional work involved. Routing, when needed, must be done with extreme care lest the edges of a figure be marred, and this work requires skill that can be gained only by experience.

Copy for the half-tone process should be as nearly perfect as possible. Only the best photographs should be selected. Prints on semimat velox and glossy haloid papers are regarded as the best photographic copy for reproduction. Every part of the photograph or drawing should be absolutely clean. If any part that should be pure white becomes soiled or stained the defects will be reproduced. If a photograph needs retouching it should be retouched with great care and just sufficiently to correct defects and to bring out or strengthen the important details. In many photographs the skies may be "muddy" or uneven in tone, and this defect can be corrected by the use of an air brush, the only medium that will produce an almost even tone. As already stated, half-tone plates can be improved by re-etching and tooling, but tooling tends to destroy the effects of nature and produces an artificial appearance in the print. One who is preparing wash drawings for reproduction by the half-tone process should remember that brush marks and other inequalities of tone will be reproduced with as much fidelity as other details. Such drawings should therefore be made two or three times larger than the engraved cut in order to subdue all unnatural effects and to soften the general tones.

Line drawings are not generally suitable copy for the half-tone process, but it is occasionally desirable to use that process instead of zinc etching for reproducing a line drawing that has been inexpertly prepared if the cost of redrawing would more than offset the difference in cost between zinc etching and the more expensive half-tone process. In reproducing a pen drawing by half tone the lines become softened and represent the details and shading only; but the pen drawing may be further developed by brush work. Examples of this type of reproduction are Plates V, _A_, VI, _A_, and XV, figure 10, and other illustrations in Survey Monograph 34.

Vignetting, which consists of a skillful grading off of the edges of a picture, as well as extensive tooling or hand engraving, is often employed for artistic effect but should be specified only for exceptional illustrations. The plates made for the Survey are either "square trimmed" or the ground tint is entirely omitted or routed away; they are not usually tooled or vignetted.

Half-tone cuts etched on copper cost 20 to 60 cents a square inch, the cost being varied according to a standard scale based on the ascertained cost of reproduction. Those that require a screen finer than 150 lines cost 25 per cent additional. The minimum charge for a single cut is $3.

Half tones etched on zinc (100-line screen or coarser) cost 25 per cent less than those etched on copper.

THREE-COLOR HALF-TONE PROCESS.

The three-color process is practically an adaptation of the half-tone process to color printing based on the theory that all colors or hues in nature can be reproduced by combinations of three colors of the spectrum--red, blue, and yellow. The process differs from the ordinary half-tone process particularly in the use of color filters in making the negatives and in the character of screens and diaphragms used. This process, like all others, is worked somewhat differently in different establishments. In what is called the indirect method, the one most commonly used, twelve photographic operations are necessary to produce one illustration, or the three plates or cuts from which one illustration is to be reproduced by printing. These twelve operations produce three chromatic negatives, each representing one color; three transparencies or positives, made from the chromatic negatives; three half-tone negatives, made from the positives; and finally three contact prints, made on sensitized metal plates. In what is called the direct method the half-tone screen is placed in front of the photographic plate so that it becomes also a half-tone negative from which a print is made on a sensitized metal plate. Thus the photographic operations in the direct method are reduced to six, but the interference to the passage of light offered by the half-tone screen and by the prism used to reverse the image on the negative lengthens the time of exposure.

Unfortunately, no pigments have been found that can reproduce in purity the colors of the spectrum, and to this fact is due the failure of the process to reproduce exactly all the colors, tints, and shades of an original. When a drawing in black on white paper is photographed only the white paper affects the negative film. The transparent parts of the developed negative thus represent the black, and the opaque parts, which have been acted upon by light, represent the whits. Theoretically, when a chromatic negative is made for the yellow plate a purple-violet filter cuts out all the yellow and allows the red and blue rays to affect the plate; when a negative is made for the blue plate an orange filter similarly cuts out the blue and allows the yellow and red rays to affect the plate; and when a negative is made for the red plate a green filter cuts out the red and permits the blue and yellow rays to affect the plate. These color filters, which are usually made of transparent stained gelatin, are generally placed in front of the lens. When printing plates like those used in the half-tone process have been made from the three negatives and the plates have been inked with yellow, blue, and red ink, respectively, a combined impression from them will produce a close approximation of the subject photographed. The colored inks often used are light yellow, peacock or prussian blue, and bright, transparent crimson.

The ordinary half-tone screen, which bears lines cut at an angle of 45° to the sides of the plate, is rectangular, but the screens used for three-color work are made circular in order that they may be turned in the camera to make the lines intersect at other angles, the angles being varied to avoid producing an undesirable pattern or a moire effect. Turning the screen also prevents the exact coincidence or superposition of the red, blue, and yellow dots, which would produce black. In other respects the screens do not differ essentially from those used in ordinary half-tone work.

As special experience is necessary in printing three-color plates the engraver generally delivers the printed illustrations to the purchaser instead of the plates, which he furnishes for other kinds of relief printing.

The copy for this process may consist of anything in color, such as specimens, objects, paintings, or properly colored photographs. The process does not usually reproduce all the colors and tints of an original with equal exactness and is not used by the Survey for work that demands precise reproduction of color, but it is satisfactory for reproducing most colored drawings, colored photographs of specimens, or the specimens themselves if they show individual variations in color. As the process is entirely photomechanical it gives more scientific accuracy in detail than chromolithography, in which there is much hand work, and it is much less expensive. If the colors shown in proofs are not satisfactory they can be modified.

The four-color process, in which four color plates are used, gives a closer approximation of true color values than the three-color process, and at a comparatively small increase of cost. The additional color used is generally a neutral gray or black.

WAX ENGRAVING (THE CEROTYPE PROCESS).

The wax or cerotype process does not require finished drawings and is especially suitable for making text illustrations and small maps, although it may be used also for large work. For this process blue prints, pencil sketches, old prints, or rough copy of any kind may be submitted--that is, it is not necessary to furnish carefully prepared drawings in black ink, as it would be for photo-engraving, for the wax engraver will reproduce in proper form any illustration in which the copy and the instructions show what is wanted, just as an experienced draftsman will make a good drawing from the rough original furnished by an author. Full and clear instructions should always be given, however, as to the size of the cut wanted and what it is to show.

In this process a polished copper plate is coated with a film consisting of beeswax, a whitening medium, and other ingredients, and the coating, which varies in thickness according to the nature of the copy, is sensitized as in the ordinary photographic processes. The map or other design to be engraved is first photographed to publication size and a contact print is made on the wax coating from the negative. The lines and other parts of the photographed image are then traced or cut through the wax to the copper plate with steel tools and straightened or perfected by the engraver, but the lettering is set in printer's type, which is pressed into the wax until it also touches the metal plate. After the work of cutting through the wax has been completed the larger open spaces between the lines are "built up" by the addition of wax to give greater depth to the plate, so that the wax plate thus built up corresponds to an electrotype mold. The plate is then dusted with powdered graphite and suspended in a solution containing copper, where by electrolytic action a copper shell is formed over its surface. When this shell is sufficiently thick it is removed from the solution and reinforced on the back with metal, and proofs are taken from it. If the proofs are satisfactory the plate is blocked type-high.

Wax-engraved plates may be used for printing colored maps or diagrams, in which variations of tint are produced by various kinds of machine rulings. The effect of some of the colors thus produced is almost a "flat" tint, in which a pattern can be detected only by close scrutiny. Some color work is printed from a wax base plate in combination with half-tone color plates.

The price of a wax engraving depends entirely on the size of the cut, the amount of work involved, and the character of the original copy, but it should not exceed very much the cost of a carefully prepared pen drawing plus the cost of a zinc etching made from it. Cuts engraved by the wax process, like zinc and half-tone plates, are delivered to the purchaser. If colored work is ordered, however, the printed sheets, not the cuts, are delivered.

WOOD ENGRAVING.

Wood engraving was once the universal method of producing cuts for illustrations that were designed to be printed on an ordinary press. It is said to be the oldest of all methods of engraving illustrations. The engraving is made on a block of boxwood, a very dense, hard wood of a light-yellow color. The block is cut type-high across the grain, and the engraving surface is made perfectly smooth by nibbing it with pumice or other stone. When a cut is to be larger than 3 or 4 inches square the wood block is made up of pieces securely dovetailed or joined together to prevent splitting and warping. A woodcut is not used for printing but is electrotyped and the electrotype is used in the press.

Originally the smoothed surface of the wood block was coated with prepared chalk or Chinese whits, and on this coating a finished drawing was made with a brush and pencil by an illustrator. According to more recent practice the surface of the wood is covered with a sensitized coating, on which the drawing or design to be engraved is photographed. The engraver then, with various kinds of gravers and other tools, cuts out the parts of the picture that are to be represented by white paper and leaves the lines, dots, and black areas as a printing surface, thus translating the shades and tints of the picture into a system of lines and dots which exactly duplicate, in effect, the details and tones of the original design. In order to produce a line effect of an area in which the tone is intermediate between whits and black the engraver must space his lines so that one-half the area will remain as printing surface and the other half as white spaces, and he must give character and direction to his lines, so that, if he is skillful, he can reproduce not only the delicate tones but the texture and details of the original picture. Many wood engravers became noted for their artistic rendering of magazine illustrations, of famous paintings, and of other works of art.

The Survey began to abandon this method of engraving in 1884, when the Sixth Annual Report was in press, substituting for it the cheaper photomechanical processes, zinc etching and half-tone engraving, and entirely abandoned its use in 1892.

Many good examples of wood engraving may be found in the early monographs and annual reports of the Geological Survey. Monograph 2 contains numerous examples.

PHOTOGELATIN PROCESSES.

Bichromatized gelatin is used in several photomechanical processes of reproducing illustrations, but in the photogelatin processes the gelatin not only receives the image by exposure to light through a negative but becomes a printing surface on a plate from which prints are made somewhat as in lithography. The several photogelatin processes are much the same as the original collotype process and are best known by the names collotype, heliotype, albertype, artotype, and the German name lichtdruck.

In working these processes a thick plate of glass, after certain preliminary treatment, is coated with sensitized gelatin. The plate is then placed in a drying room or oven having a temperature of 120° F., baked until it is thoroughly dry, and allowed to cool gradually. The subject to be reproduced is then photographed in the usual manner, and unless a prism or mirror box has been used the negative is stripped and reversed in order to make the print reproduce the original in proper position. From the negative a contact print is made on the gelatin-coated plate, the parts or molecules of gelatin being hardened in proportion to the amount of light that affects them. After the contact print has been made the gelatin plate is thoroughly washed in cold water, in order to dissolve and wash out the bichromate and stop any further action of light on the plate, and is then thoroughly dried. Before prints are made from the gelatin-coated plate water is flowed on it and penetrates different parts of the gelatin according to their hardness. The darkest parts of the picture will correspond to the hardest and densest parts of the gelatin, which will not absorb water; the lighter parts will take up more water. The surface water is then removed with a rubber straight edge and an absorbent roller and the plate is ready for inking. The ink, being greasy, has no affinity for water, and when it is rolled over the plate it adheres only to the dry parts of the gelatin, and in the press is carried to the paper in all the lights and shades of the illustration. The plate is kept moist in printing.

The paper used for printing from photogelatin plates must be free from chemicals that will affect the gelatin. A nearly pure rag paper is generally used.

The photogelatin process is well adapted to the reproduction of paleontologic drawings, wash drawings, photographs, photomicrographs, works of art, old manuscripts--in fact, any kind of subject in which the reproduction of delicate lights and shades is essential. If properly manipulated it has distinct advantages over the half-tone process in that it can reproduce details and light and shade without showing the effect of a screen and without the use of coated paper. Excellent reproductions by the heliotype process are also made in color by first printing the design in a neutral tone and superposing appropriate transparent colors on this print, somewhat as in chromolithography, so that the colors softly blend with the shaded groundwork.

Reproductions made by the photogelatin process are more expensive than those made by the half-tone process, for the prints are generally made on better paper and are printed with greater care. They give no screen effect and are perhaps unrivaled by prints obtained by any other process except photogravure, in which the image is printed from a metal plate that has been sensitized, exposed under a reversed negative, and etched.

Changes can not be made on photogelatin plates except by making over the corrected parts. All retouching must be done on the originals or on the negatives made from then.

LITHOGRAPHY.

ORIGINAL PROCESS.

The general term "lithography" is sometimes used to indicate not only the original process so named, said to have been invented by Senefelder, but chromolithography, photolithography, and engraving on stone, as well as engraving on copper as a means of supplying matter to be transferred to and printed from a lithographic stone.

Senefelder discovered that limestone will absorb either grease or Water, and that neither one will penetrate a part of the surface previously affected by the other. He found that if a design is drawn on limestone with a greasy crayon and the stone afterward properly prepared with a solution of nitric acid and gum, greasy ink will adhere only to the parts that are covered with the crayon, and that the stone will give off an impression of the design.

Lithographic stone is described as a fine, compact, homogeneous limestone, which may be either a pure carbonate of lime or dolomitic--that is, it may contain magnesium. Although limestone is one of the most common rocks, limestone of a quality suitable for use in lithography is found at only a few localities.[11] There are two general classes of lithographic stone, known to the trade as "blue" or hard stone and "yellow" or soft stone. The blue stone is adapted for engraving and to the better grade of fine-line printing; the yellow stone is rated as somewhat inferior.

[Footnote 11: Kubel, S. J., Lithographic stone: U. S. Geol. Survey Mineral Resources, 1900, pp. 869-873, 1901.]

In the original process, which may here be termed plain lithography, two methods are employed in putting on stone the design to be reproduced. In one the subject or picture to be reproduced is drawn on the printing stone either with a lithographic crayon or with a pen dipped in lithographic ink or "tusche," which is oily or fatty, like the crayon. In the other method the drawing is made on transfer paper and transferred to the stone. In drawing on stone it is necessary to reverse the design, so that all lettering must be drawn backward. In doing this the artist often uses a mirror to aid him. If the drawing is made on transfer paper the design and the lettering are copied as in the original--not reversed.

Before a drawing is made on stone a stone of the quality suited to the particular design in hand is selected. The stone is then ground and polished, and if the drawing is to be made with crayon it is "grained" according to the special requirements of the subject. If the drawing is to be made with a pen and is to consist of "line work" the stone is polished. The first step is to obtain on the stone an outline or "faint" of the design. There are several ways to do this. By one method a tracing of the design is made, a sheet of thin paper covered with red chalk is laid face downward on the stone, the tracing is laid face downward over it, and the design is again traced in red-chalk lines on the stone. The method described is simple, but there are others that are more complicated and that are particularly applicable to the reproduction of photographs and other illustrations. Crayon work is often used in combination with pen and ink, stipple, and brush work. This method of drawing on stone is used also for preparing color stones in the process of chromolithography, in which there are many added details of manipulation. After the drawing has been made on the stone or transferred to it the stone is "gummed"--that is, it is covered with a solution of gum arabic and nitric acid--and dried. The stone is then dampened with water and carefully rolled with lithographic ink, which adheres to the pen or crayon work and is repelled elsewhere. It is then "rubbed" over with powdered rosin and talcum, which adheres to the ink and further protects the drawing from the effects of the etching fluid, which is next to be applied to the stone. This fluid consists of a 10 per cent solution of gum arabic to which 2 to 7 per cent of nitric acid has been added, the degree of acidity being varied according to the subject and the hardness of the stone. The fluid is applied with a brush or sponge and is left on the stone just long enough to decompose slightly the carbonate of lime on its surface and, after washing, to leave the design or drawing in very slight relief. The stone is again gummed and dried, and the design is "washed out" or brought out by removing the surface gum with a wet sponge and applying to the stone a rag sprinkled with turpentine and charged with printing ink. These operations wash away the tusche and the crayon that have been decomposed by the acid and expose the design faintly in white at first, but it gradually grows darker as it becomes charged with printing ink from the rag. The stone is next "rolled up" or inked. The slightly moistened surface repels the ink and the design takes it up, so that when the stone is run through the press the design is carried to the paper.

Lithographic prints from stones prepared in this way are made on a flat-bed press. The stone is carried forward to print and on its return is dampened and inked, an operation slower than that of rotary printing.

Corrections and changes are made on the stone by carefully scraping or polishing away the parts to be corrected and making the changes with a crayon or pen, but the design can not ordinarily be corrected twice in the same place, as the scraping or polishing removes a part of the surface of the stone and thus lessens the pressure at that place, and the impression there may be imperfect or may completely fail.

This form of lithography is seldom used for Survey illustrations but was formerly much used and is well adapted to the reproduction of drawings of fossils, particularly of remains of dinosaurs and other types of large extinct animals. Examples may be seen in Monographs 8 and 10 and in other early reports of the Geological Survey. The drawings for these illustrations were made directly on stone.

A drawing made on one stone may be transferred in duplicate or in any desired number to another stone, or to a properly grained sheet of zinc and aluminum, from which impressions may be printed on a lithographic press. Both these metals are also used for lithographic printing on rotary presses, the zinc or aluminum plate being bent and secured around a cylinder which rotates continuously in one direction. As one impression is made at each revolution of the cylinder the printing is rapid; but the best printing from a metal plate is inferior to the best printing from a lithographic stone.

PHOTOLITHOGRAPHY.

Photolithography, like other lithographic processes, has been improved greatly during the last few years--not particularly in results but in methods--by the introduction of metal plates, the rubber blanket offset, the Ben Day films, and many mechanical and chemical devices, so that a brief description of it will not explain the process except in a most general way. As photolithography is a direct process and is relatively cheap it is the one most used for reproducing large maps and other line drawings that have been carefully prepared. Zinc and aluminum plates are now much used in photolithography, for a direct contact photographic print can be made on them, they can be printed flat or bent for use on a rotary press, and they can be stored for future use more economically than stones.

There are two somewhat distinct methods of producing photolithographs. In both the ordinary photographic methods are used, but it is often necessary to "cut" or trace parts of the negative in order to open up lines and other features that are not sharp or well defined, so that the negative will print them sharp and clear. If the copy to be reproduced shows three colors, three negatives are made, one for each color, and the parts to be shown by each are preserved by "opaquing" or painting out all other parts. By the older method the negative thus perfected is placed in a printing frame in contact, under pressure, with sensitized transfer paper and is exposed to light. The printing frame is then carried to the dark room and the paper is removed from the frame and its surface covered with transfer ink. The paper is then laid face upward on water and soaked for several minutes, after which it is placed in the same position upon a slab of stone or metal and thoroughly washed with water. This washing removes the ink and the sensitive film from the parts that were unaffected by the action of light (the parts corresponding to the white paper in the design), but the ink still adheres to the lines of the design in the precise sharpness and clearness of the negative. The design is now ready to be transferred to the printing stone or zinc plate. The sheet is again slightly dampened between moist blotters and laid face downward in its correct position on a prepared stone or zinc plate, which is then pulled through a press under heavy pressure. The paper is then removed from the stone or plate, to which it has carried the design. From this point the gumming, etching, and other operations are practically the same as those used in ordinary lithography.

The bichromate-gelatin transfer process described above has been replaced in the Survey by a more satisfactory one, which insures absolute scale and reproduces the finest line drawings perfectly without thickening the lines or without distortion. In this process, which is known as the planographic process, a photographic negative of the "copy" is placed in a vacuum printing frame in contact with a zinc or aluminum plate that has been sensitized with a bichromate-albumen solution and exposed in front of an arc lamp. After proper exposure the plate is removed from the frame, inked over, and placed under water. The parts not hardened by the action of light (the unexposed parts) are then rubbed away with cotton, and the plate is chemically etched, gummed over, and dried. The plate is then ready to be printed from in a lithographic press. If a large map is to be reproduced it is photographed in parts, and contact prints are made on zinc plates. From these plates transfers are pulled and the parts are assembled and laid down in proper position on a stone or an aluminum plate, which is then prepared for printing.

A drawing that is to be reproduced by photolithography should be made on pure-white paper in lines, dots, or black masses with black waterproof ink. It should be one and one-half to two or three times the size of the finished print.

Photolithography is particularly adapted to the reproduction of maps, plans, and other large drawings. Within certain limitations, lines may be changed and details may be added after proofs have been submitted. The process is ordinarily used for reproducing illustrations in one color (black), but it is used also for printing in more than one color, generally over a black outline base, each color being printed from a separate stone, as in chromolithography.

OFFSET PRINTING.

In the offset process the design is "offset" from a lithographic plate or stone to a rubber blanket on a cylinder, from which it is printed. By thus obtaining an impression from an elastic surface the finest details can be printed on rough, uncoated paper, which can not be used in other processes, which can be folded without danger of breaking, and which is more durable than coated paper. Plates II, III, IV, VII, and VIII in this pamphlet were printed by this process.

CHROMOLITHOGRAPHY.

The chromolithographic process, by which illustrations are printed in color from stone, is used in Survey publications principally for reproducing geologic maps, but it is sometimes used for reproducing colored drawings of specimens.

There are several kinds of color printing from stones. One produces a picture by superimposing colors that combine and overlap without definite outlines and thus reproduce the softly blended colors of the original. Another reproduces the original by printing colors within definite outlines on a "base" which has been previously printed in black. The first kind is used by the Survey for reproducing colored drawings of specimens. The second is followed in reproducing geologic maps.

As each color must be printed from a separate stone and properly fitted with respect to the others a tracing from the original is made of the precise outlines of each color; or, if the design is to be reduced, a tracing is made over a properly reduced photographic print. This tracing can be made on specially prepared tracing paper or on a sheet of transparent gelatin or celluloid, which is laid over the copy and on which all the outlines and overlaps of the various colors are scratched with a steel point. The scratches thus made on the celluloid are filled with red chalk or like substance, and rubbed in with cotton, and by reversing the sheet and rubbing it the chalk lines are deposited on as many stones as are needed to produce the colors of the original design, each stone bearing all the outlines of the design. Sometimes all the outlines are engraved on what is called a key stone and an impression from it is laid down on each of the color stones. The parts on each stone that are to have one color are then inked in or engraved, and at the same time guide marks are indicated, so that in the composite print from the stones each color will fit its proper place. This fitting is called "register" and is an important part of printing, for each stone must be adjusted to a nicety while on the press in order to make each impression fit the others exactly. The process was originally manipulated entirely by hand, but photography has now replaced much of the handwork and has given rise to several methods by which the same kinds of subjects are reproduced in radically different ways. Tints are sometimes produced by the half-tone and other screens and by machine ruling, and printer's type is used almost exclusively for titles and other matter that was formerly engraved or drawn on the stone.

In reproducing a geologic map the base may be engraved on stone or on copper or it may be photo-lithographed. By either process the map may be transferred to the printing stone. The color stones for geologic maps are prepared by hand, but the geologic patterns, which are printed in colors, are engraved separately on plates, from which impressions are pulled when needed and transferred to their proper places on the printing stones in the shapes required according to the "key" design. The lighter, more transparent colors are generally printed first, and often twelve or more colors and many distinctive patterns are used to produce a geologic map. When proofs of such a map are pulled each stone must be taken up and carefully adjusted on the press, so that the work of proving maps that are printed from a considerable number of color stones is laborious and expensive. It is therefore customary to approve first combined proofs conditionally--that is, subject to the corrections and changes indicated on the proofs--and to hold the lithographer responsible for any failure to make the corrections.

This process is the most expensive one used for reproducing illustrations. Changes may be indicated on proofs, but changes can not be made on a stone twice in the same place without danger of affecting the printing or making it necessary to retransfer the parts affected. All changes are expensive because a slight modification at one point may involve corresponding changes on a number of stones, each of which must be taken up, corrected, and proved to insure the exact coincidence of the parts affected. It is often less expensive to retransfer the entire job than to make extensive changes on the original stones.

ENGRAVING ON STONE AND ON COPPER.

Engraving on stone is distinctly lithographic, but engraving on copper is sometimes included among lithographic processes because the work produced by it is usually printed from stone and thus becomes lithographic. In other respects engraving on copper is not a lithographic process. Roughly prepared maps and any rough line copy that is accurate in statement and clear as to intent are appropriate for both methods of engraving, but drawings that are expertly prepared are more suitable for reproduction by photolithography. In engraving on stone the lines of a design are scratched on the blackened surface of a stone with a steel-pointed tool; in engraving on copper the lines are cut with a graver on a sheet or plate of copper, the matter to be engraved being first shown on the plate by what is called the photo-tracing process, which was devised in the Geological Survey. There is, however, no great or essential difference in the printed results of the two processes, but most lithographers employ only stone engravers.

A stone on which a design is to be engraved is ground and polished according to the kind of work to be engraved, is coated with a thin solution of gum arable and allowed to dry, and is then washed until the superficial gum is removed while the surface pores remain filled. As the lines made by the engraver must be visible the stone is blackened with a pigment composed of lampblack and gum or is covered evenly with red chalk or Venetian red. It is then ready to receive the design to be engraved.

If the design is a map which is to show culture, streams, and surface contours, and each of these sets of features is to be printed in a separate color, impressions of the work to be engraved must be placed on three stones. One method of doing this is to make a scratch tracing of the original drawing on a sheet of transparent gelatin or celluloid in the manner employed in chromolithography, except that a dry pigment, generally chrome-yellow, is used to fill the scratch lines instead of red chalk or Venetian red. From this tracing a "faint" or imprint of all the details of the three separate features of the map is made on each of the three stones, and the engraver then cuts on each stone only the lines and other features, including ample register marks, that are to be printed in one color, the imprint made from the tracing making it possible to engrave each set of features in its exact position relative to the other two. By another method the matter to be engraved is photographed directly on the stone.

The engraving is done with a steel needle inserted in a small wooden cylinder, an instrument resembling an ordinary lead pencil. The size and shape of the needles used are varied according to the requirements of the matter to be engraved. With this instrument the lines and lettering are lightly scratched into the stone through the dark coating and show as light lines. The points of some of the needles are fine; those of others are V-shaped; and some have spoon-shaped points, for use in thickening lines and shading letters. All features are engraved in reverse.

After the engraving is completed the stones are prepared for printing by wiping off all the superficial color and filling the engraved lines with a greasy ink--generally a thin printing ink--which is rubbed into the lines with a soft rag. Impressions are then pulled on transfer paper and transferred to three printing stones for use in printing the three colors, the register marks enabling the pressman to fit each color exactly in its proper place.

In all lithographic processes the titles and other marginal lettering can be and usually are transferred from type impressions to the printing stones. It is therefore unnecessary to letter such matter carefully on an original drawing that is made for lithographic reproduction, for appropriate faces of type will give better printed results than hand lettering.

Corrections can not be made on a stone or copper engraving as readily as on a drawing. If a stone engraver makes an error or if a change is required after his engraving is finished, the parts to be corrected must be scraped off and a new ground laid before the correction can be made. Sometimes he will engrave the parts corrected on another part of the original stone and transfer it to the printing stone. Corrections are made on copper plates by "hammering up" the plate from beneath, polishing off a new surface, and reengraving the part to be corrected.

APPENDIX.

The matter given in this appendix is much used in making geologic maps and other illustrations. The Greek alphabet and the groups of signs presented are given chiefly to show the correct formation of each letter and sign.

MISCELLANEOUS TABLES.

_Length of 1° of longitude measured along given parallels from the Equator to the poles._

[From U. S. Coast and Geodetic Survey Report for 1884, Appendix 6.]

Parallel of Statute | Parallel of Statute | Parallel of Statute latitude. miles. | latitude. miles. | latitude. miles. ----------------------+-----------------------+---------------------- 0 69.172 | 31 59.365 | 61 33.623 1 69.162 | 32 58.716 | 62 32.560 2 69.130 | 33 58.071 | 63 31.488 3 69.078 | 34 67.407 | 64 30.406 4 69.005 | 35 66.725 | 65 29.315 5 68.911 | 36 66.027 | 66 28.215 6 68.795 | 37 65.311 | 67 27.106 7 68.660 | 38 64.679 | 68 26.988 8 68.504 | 39 63.829 | 69 24.862 9 68.326 | 40 53.063 | 70 23.729 10 68.129 | 41 62.281 | 71 22.589 11 67.910 | 42 51.483 | 72 21.441 12 67.670 | 43 60.669 | 73 20.287 13 67.410 | 44 49.840 | 74 19.127 14 67.131 | 45 48.995 | 75 17.960 15 66.830 | 46 48.136 | 76 16.788 16 66.510 | 47 47.261 | 77 15.611 17 66.169 | 48 46.372 | 78 14.428 18 65.808 | 49 45.469 | 79 13.242 19 65.427 | 50 44.652 | 80 12.051 20 65.026 | 51 43.621 | 81 10.857 21 64.606 | 52 42.676 | 82 9.659 22 64.166 | 53 41.719 | 83 8.458 23 63.706 | 54 40.749 | 84 7.256 24 63.228 | 55 39.766 | 85 6.049 25 62.729 | 56 38.771 | 86 4.842 26 62.212 | 57 37.764 | 87 3.632 27 61.676 | 58 36.745 | 88 2.422 28 61.122 | 59 35.716 | 89 1.211 29 60.548 | 60 34.674 | 90 .000 30 59.956 | |

_Length of 1° of latitude measured along a meridian at given parallels._ [Parallel given is in center of the degree whose length is stated.]

Parallel of Statute latitude. miles. ---------------------- 0 68.704 10 68.725 20 68.786 30 68.879 40 68.993 50 69.115 60 69.230 70 69.324 80 69.386 90 69.407

Metric system and equivalents.

[The units of linear measure most commonly used are millimeters (mm.), centimeters (cm.), decimeters (dm.), meters (m.), and kilometers (km.), 1 m. = 10 dm.; 1 dm. = 10 cm.; 1 cm. = 10 mm.; 1 km. = 1,000 meters = 0.62137 mile; 1 m. = 39.37 inches = 3.280833 feet.]

Meters. | Inches. || Meters. | Feet. || Kilometers. | Miles. ----------+-------------++---------+-----------++-------------+--------- 1 | 39.37 || 1 | 3.280633 || 1 | 0.62137 2 | 78.74 || 2 | 6.561667 || 2 | 1.24274 3 | 118.11 || 3 | 9.842500 || 3 | 1.86411 4 | 157.48 || 4 | 13.123333 || 4 | 2.48548 5 | 196.85 || 5 | 16.404166 || 5 | 3.10685 6 | 236.22 || 6 | 19.685000 || 6 | 3.72822 7 | 275.59 || 7 | 22.965833 || 7 | 4.34959 8 | 314.96 || 8 | 26.246666 || 8 | 4.97096 9 | 354.33 || 9 | 29.527500 || 9 | 5.59233

Inches. | Centimeters.|| Feet. | Meters. || Miles. | Kilometers. ----------+-------------++---------+-----------++-----------+------------ 1 | 2.54 || 1 | 0.304801 || 1 | 1.60935 2 | 5.08 || 2 | 0.609601 || 2 | 3.21869 3 | 7.62 || 3 | 0.914402 || 3 | 4.82804 4 | 10.16 || 4 | 1.219202 || 4 | 6.43739 5 | 12.70 || 5 | 1.524003 || 5 | 8.04674 6 | 15.24 || 6 | 1.828804 || 6 | 9.65606 7 | 17.78 || 7 | 2.133604 || 7 | 11.26543 8 | 20.32 || 8 | 2.438405 || 8 | 12.87478 9 | 22.86 || 9 | 2.743205 || 9 | 14.48412

The "vara," used in Texas, is equivalent to 33-1/3 inches and is computed as representing 2.78 feet.

_Geologic eras, periods, systems, epochs, and series._

Era. Period or system. Epoch or series.

{ { Recent. { Quaternary. { Pleistocene (replaces "Glacial"). Cenozoic. { { { Pliocene. { Tertiary. { Miocene. { { Oligocene. { { Eocene.

{ { Upper (Gulf may be used { { provincially). { Cretaceous. { Lower (Comanche and Shasta may be { { used provincially). { { { Upper. Mesozoic. { Jurassic. { Middle. { { Lower. { { { Upper. { Triassic. { Middle. { { Lower.

{ { Permian. { { Pennsylvanian (replaces "Upper { Carboniferous. { Carboniferous"). { { Mississippian (replaces "Lower { { Carboniferous"). { { { Upper. { Devonian. { Middle. { { Lower. { Paleozoic. { Silurian. { { { Upper (Cincinnatian may be used { { provincially). { Ordovician. { Middle (Mohawkian may be used { { provincially). { { Lower. { { { Saratogan (or Upper Cambrian). { Cambrian. { Acadian (or Middle Cambrian). { { Waucoban (or Lower Cambrian).

{ Algonkian. }pre-Cambrian. Proterozoic. { Archean. }

_Chemical elements and symbols._

Element. Symbol. Element. Symbol. Element. Symbol.

Aluminum Al Holmium Ho Rhodium Rh Antimony Sb Hydrogen H Rubidium Rb Argon Al Indium In Ruthenium Ru Arsenic As Iodine I Samarium Sa Barium Ba Iridium Ir Scandium Sc Bismuth Bi Iron Fe Selenium Se Boron B Krypton Kr Silicon Si Bromine Br Lanthanum La Silver Ag Cadmium Cd Lead Pb Sodium Na Cesium Cs Lithium Li Strontium Sr Calcium Ca Lutecium Lu Sulphur S Carbon C Magnesium Mg Tantalum Ta Cerium Ce Manganese Mn Tellurium Te Chlorine Cl Mercury Hg Terbium Tb Chromium Cr Molybdenum Mo Thallium Tl Cobalt Co Neodymium Nd Thorium Th Columbium C Neon Ne Thulium Tm Copper Cu Nickel Ni Tin Sn Dysprosium Dy Niton Nt Titanium Ti Erbium Er Nitrogen N Tungsten W Europium Eu Osmium Os Uranium U Fluorine F Oxygen O Vanadium V Gadolinium Gd Palladium Pd Xenon Xe Gallium Ga Phosphorus P Ytterbium Germanium Ge Platinum Pt (Neoytterbium) Yb Glucinum Gl Potassium K Yttrium Y Gold Au Praseodymium Pr Zinc Zn Helium He Radium Ra Zirconium Zr

_Greek alphabet._

Caps. Lower-case. Greek name. English sound. [Greek: A] [Greek: a] Alpha. A. [Greek: B] [Greek: b] Beta. B. [Greek: G] [Greek: g] Gamma. G. [Greek: D] [Greek: d] Delta. D. [Greek: E] [Greek: e] Epsilon. E short. [Greek: Z] [Greek: z] Zeta. Z. [Greek: H] [Greek: h] Eta. E long. [Greek: Th] [Greek: th] Theta. Th. [Greek: I] [Greek: i] Iota. I. [Greek: K] [Greek: k] Kappa. K. [Greek: L] [Greek: l] Lambda. L. [Greek: M] [Greek: m] Mu. M. [Greek: N] [Greek: n] Nu. N. [Greek: X] [Greek: x] Xi. X. [Greek: O] [Greek: o] Omicron. O short. [Greek: P] [Greek: p] Pi. P. [Greek: R] [Greek: r] Rho. R. [Greek: S] [Greek: s] Sigma. S. [Greek: T] [Greek: t] Tau. T. [Greek: U] [Greek: u] Upsilon. U. [Greek: F] [Greek: f] Phi. F. [Greek: Ch] [Greek: ch] Chi. Ch. [Greek: Ps] [Greek: ps] Psi. Ps. [Greek: Om] [Greek: om] Omega. O long.

_Roman numerals._

I 1 | IX 9 | LXX 70 | D 500 II 2 | X 10 | LXXX 80 | DC 600 III 3 | XIX 19 | XC 90 | DCC 700 IV 4 | XX 20 | C 100 | DCCC 800 V 5 | XXX 30 | CL 150 | CM 900 VI 6 | XL 40 | CC 200 | M 1000 VII 7 | L 50 | CCC 300 | MD 1500 VIII 8 | LX 60 | CD 400 | MCM 1900

Mathematical signs.

+ plus. ~ difference - minus. integration. × multiplied by. equivalence. ÷ divided by. : ratio. = equality. geometrical proportion. ± plus or minus. -: difference, excess. square. therefore. rectangle. because. triangle. infinity. circle. varies as. angle. radical. right angle. ° degree. or > greater than. ' minute. or < less than. " second. perpendicular.

NAMES OF ROCKS.

The following list was prepared in the geologic branch for the use of geologic draftsmen to enable them to select appropriate symbols for rocks that may be referred to in preliminary drawings by name only. For sedimentary rocks dots and circles, parallel lines, and broken or dotted lines are used; for metamorphic rocks short dashes arranged without definite patterns; and for igneous rocks patterns composed of short dashes, triangles, rhombs, crosses, and cross lines. All these patterns are shown in Plate III.

_Sedimentary material._

[Including residual, detrital, eolian, glacial, organic, and chemically precipitated material.]

Agglomerate. Ironstone (also igneous). Alabaster. Itacolumite. Alluvium. Kame. Alum shale. Kaolin. Anhydrite. Laterite. Apron (alluvial). Lignite. Argillite. Limestone. Arkose. Limonite. Asphalt. Loess. Bench gravel. Marble (also metamorphic). Bentonite. Marl. Boulder clay. Metaxite. Brea. Morainal deposit. Breccia. Mudstone. Brownstone. Novaculite. Burrstone. Peat. Calcarenite. Pelite. Calc sinter. Phosphate rock. Caliche. Phosphorite. Catlinite. Phthanite. Chalk. Psammites. Chert. Psephites. Clay. Puddingstone. Coal. Pyroclastic material. Conglomerate. Quartzite (also metamorphic). Coprolite. Reddle. Coquina. Rock salt. Detritus. Rock stream. Diatomaceous earth. Rubble. Diluvium. Salt. Dolomite. Sand. Drift. Sandstone. Fan (alluvial). Selenite. Fanglomerate. Shale. Flagstone. Silt. Flint. Slate (also metamorphic). Freestone. Soil. Fuller's earth. Stalactite. Geyserite. Stalagmite. Gravel. Talc. Graywacke. Talus. Greensand. Till. Grit. Travertine. Gumbo. Tripoli. Gypsum. Tufa (=chemically deposited lime). Hardpan. Tuff (=igneous fragments). Hematite. Wacke. Infusorial earth. Wash.

_Metamorphic material._

Adinole. Hornstone. Amphibolite. Itabirite. Andalusite schist (?). Kinzigite. Apo (rhyolite), etc. Knotenschiefer. Argillite. Knotty schists. Augen gneiss (also igneous). Luxulianite (igneous?). Biotite schist. Marble. Calc schist. Meta (diabase), etc. Cataclastic. Mica schist. Chlorite schist Mylonite. Clay slate. Ophicalcite. Damourite schist. Ottrelite schist. Desmosite. Phyllite. Dynamometamorphic rock. Porcelanite. Eclogite. Protogene. Epidosite. Pyroschists. Erlan. Quartz. Erlanfels. Quartzite. Eulysite. Quartz schist. Fibrolite schist Schist. Garnet rock. Sericite schist, etc. Garnet schist. Serpentine. Gneiss. Slate. Granite gneiss. Soapstone. Graywacke (?). Sodalite. Green schists. Spilosite. Greenstone (also igneous). Steatite. Greisen. Talc schist. Halleflinta. Topazfels. Hornblende schist Topaz rock. Hornfels. Zobtenite.

_Igneous material._

Absarokite. Dolerite. Abyssal. Dunite. Adamellite. Durbachite. Adendiorite. Effusive rock. Ailsyte. Ekerite. Åkerite. Elvan. Alaskite. Enstatite. Albitlte. Eruptive rock. Allivalite. Essexite. Allochetite. Estrellite. Alnölte. Eulysite. Alsbachite. Extrusive rock. Ambonite. Farrisite. Amherstite. Felsite. Analcitite. Felsophyre. Andesite. Fergusite. Anorthosite. Fortunite. Aphanitite. Fourchite. Aplite. Foyaite. Arkite. Gabbro. Atatschite. Gauteite. Augen gneiss (also metamorphic). Garewaite. Augitite. Glumarrite. Avezacite. Gladkaite. Banakite. Granite. Banatite. Granitite. Bandaite. Granitoid. Basalt. Granodiorite. Basanite. Granophyre. Beerbachite. Greenstone (also metamorphic). Bekinkinite. Greisen (?). Bombs. Grorudite. Borolanite. Harrisite. Bostonite. Harzburgite. Camptonite. Haüynophyre. Carmeloite. Hawaiite. Cascadite. Hedrumite. Chibinite. Heumite. Ciminite. Holyokeite. Comendite. Hornblendite. Complementary rocks. Hypabyssal rock. Coppaelite. Hyperite. Cortlandite. Hypersthenite. Cromaltite. Ijolite. Cumberlandite. Intrusive rock. Cuselite. Irruptive (=Intrusive) rock. Dacite. Isenite. Dellenite. Jacupirangite. Diabase. Jumillite. Diallagite. Kaiwekite. Dike rock. Kedabekite. Diorite. Kentallenite. Ditroite. Kenyite.

_Igneous material._--Continued.

Keratophyre. Perlite. Kersantite. Phanerite. Kimberlite. Phonolite. Kobalaite. Pierite. Krablite. Pitchstone. Krageröite. Plagiaplite. Kulaite. Plagioclastic. Kyschytymite. Plumasite. Lamprophyre. Plutonic rock. Latite. Pollenite. Laugenite. Porphyry. Laurdalite. Pulaskite. Laurvikite. Pumice. Lava. Pyroxenite. Lestiwarite. Rhombenporphyry. Leucite basalt. Rhyolite. Leucite tephrite. Rizzonite. Leucitite. Rockalite. Leucocratic. Santorinite. Lherzolite. Sanukite. Limbergite. Saxonite. Lindoite. Scyelite. Liparite. Shastaite. Litchfieldite. Shonkinite. Lithoidite. Shoshonite. Luciitss. Soda granite. Lujaurite. Sölvsbergite. Madrupite. Sommaite. Maenaite. Spessartite. Magma basalt. Sussexite. Malchite. Syenite. Malignite. Taimyrite. Mangerite. Tawite. Mariupolite. Tephrite. Melaphyre. Teschenite. Melilite basalt. Theralite. Mesanite. Tilaite. Mica peridotite. Tinguaite. Minette. Tjosite. Missourite. Tonalite. Monchiquite. Tonsbergite. Mondholdeite. Tordrillite. Monmouthite. Toscanite (?). Monzonite. Trachy-andesite. Mugearite. Trachyte. Naujaite. Trap. Nelsonite. Troctolite. Nephelinite. Umptekite. Nevadite. Unakite. Nordmarkite. Ungaite. Norite. Urtite. Obsidian. Valbellite. Odinite. Venanzite. Orbite. Verite. Orendite. Vitrophyre. Ornöite. Vogesite. Orthophyre. Volcanic rock. Ortlerite. Volhynite. Ouachitite. Vulsinite. Paisanite. Websterite. Pantellerite. Wehrlite. Pegmatite. Windsorite. Peridotite. Wyomingite. Perknite. Yamaskite.

INDEX.

A.

Abbreviations, forms of. 55-67 Adhesive materials, choice. 37 Alaska, maps of, reuse of. 17 Albertype. _See_ Photogelatin processes. Apparatus, photographs of, preferred to sketches. 29 Approval of finished drawings, features to be covered by. 38 of illustrations, regulations governing. 80 Areas, patterns used to distinguish. 23 patterns used to distinguish, plate showing. 62 Army, Corps of Engineers of the, maps published by. 15 Artotype. _See_ Photogelatin processes. Atlases, published, use of. 15

B.

Base maps. _See_ Maps, base. Bleaching photographic prints, method and solutions for. 69 Border for maps, width and use of. 57-58 Bristol board, kind Mid sizes used. 24,66 Brash and pencil drawings, materials and methods used in making. 66-67, 69 Brushes, kinds and sizes used. 66-67,71

C.

Celluloid transferring, process of. 47 requisitions for. 47 Cerotype process, description and advantages of. 80-81 Changes in engravings, possible kinds of. 38-39, 90 Changes in original material, draftsman to consult author on. 65 Chemical elements, names and symbols of. 98 Chromolithography, description of. 87-80 Civil divisions, lettering of. 53, 54 Coal beds, indication of thickness of. 31 Coast and Geodetic Survey charts, use of. 15 Collotype. _See_ Photogelatin processes. Coloring materials, use of. 26 Colors, standard, for geologic maps. 62-63 use of, for ground-water features. 21-23 on original geologic maps. 27-28 Commas, form of. 54 use of, in numbers. 54 Contours, drawing of. 48-50 Cooperation, mention of. 13 Copper, engraving on. 89, 90 etching in relief on, process and advantages of. 75 Copying methods of. 46-48 Corrections. _See_ Changes. Cost of photo-engravings. 75, 78, 80, 81 County maps, use of. 15 Crayons, wax, use of. 26, 50, 51 Credit for data of maps, indication of. 13 Crystals, drawings of, making and lettering of. 70 Cultural features, lettering of. 53-54 list of. 52-53 Curves, date showing. 64 Cuts. _See_ Engravings.

D.

Details of a geologic map, plate showing. 58 Diagrams, drawing and lettering of. 64 features of, plate showing. 64 original, general requirements for. 28-20 Director of the Survey, order by. 9 Divisions of plates and figures, serial letters and numbers for. 12 Drafting table, shadowless, description of. 47-48 shadowless, use of. 29, 48, 50 Draftsmen, detail of, to aid author. 9 detail of, to prepare base maps. 13-14 experience and reading required by. 41-42 general treatment of material by. 42-43 Drainage features, depiction of. 51-52 Drawing instruments, list of. 42 Drawing materials, kinds used. 23-26, 66-67, 69, 71 Drawings, authors', draftsmen may aid in making. 9 authors', editorial revision of. 38 finished, general requirements for. 41-42 requests for photographs of. 34 Duplicates of engravings, charges for. 38

E.

Effectiveness of illustrations, elements that produce. 7, 30 Electrotypes of engravings, charges for. 38 Elements, chemical, names and symbols of. 93 Engraving on stone, process of. 89-90 _See also_ Lithography. Engravings, changes in. 38-39 original, time of keeping. 37 Erasers, injury to paper by. 67 kinds used. 25, 67-68 Erasures, smoothing paper after. 68 Explanations on maps, arrangement and lettering of. 19, 58-50

F.

Figures, differences from plates. 10-11 divisions of, serial letters for. 12 methods of inserting, plate showing. 12 Formations, geologic, use of letter symbols for. 20-21 Fossils. _See_ Specimens. Four-color process, advantage of. 80

G.

Gas wells, symbols for. 21 Generalization, true, meaning of. 17 Geographic tables and formulas (Bull. 650), use of. 44, 45 Geologic periods of time, names of. 92 Gouache, use of. 67, 69 Great Lakes surveys, maps published by. 15 Greek letters, forms, names, and English sounds of. 93 Ground-water features, symbols representing. 21-23

H.

Hachuring, use of. 50 Half-tone engraving, preparation of copy for. 77-78 process and advantages of. 75-78 three-color process of. 78-80 Half tones, changes in. 39 prints of, showing effects produced by different screens. 56 requirements for printing. 11 Heliotype. _See_ Photogelatin processes. Hill shading, use of. 60-51 Hydrographic features, lettering of. 54 representation of. 51-52 Hypsographic features, lettering of. 54

I.

Illustrations, kinds of. 10-11 Inks, kinds used. 25, 67 methods of using. 25 Inserting plates and figures, methods of, plate showing. 12 Instruments, draftsmen's, list of. 42

J.

Japanese transparent water colors, use of. 26

L.

Land Office maps, scales and detail of. 14-15 Latitude, length of 1° of, at intervals of 10°. 91 Lending of photographs and drawings, rules governing. 34 Letter symbols, use of, on geologic maps. 20-21 Lettering, directions for. 53-55 for lithographing. 90 for names of streams. 52, 54 on diagrams. 64 on drawings of crystals. 70 on original maps. 19 on plans and cross sections of mines. 65-66 reduction sheet used in, plate showing. 54 use of type for. 54-55 Light, direction and gradation of. 66 Lithographs, printing and insertion of. 11 Lithography, original process of. 83-85 _See also_ Engraving on stone. Longitude, length of 1° of, at latitudes 0° to 90°. 91

M.

Map of the world, millionth-scale, use of, for base maps. 14 Maps, areal patterns for, drawing of. 61-62 bar scales for. 59-60 base, conventional symbols used on. 45-46 including new data, how obtained. 13-14 indication of sources on. 13 of the United States on small scales, use of. 15 published maps available for. 14-17 reuse of, to be approved. 13 black and whits, patterns used on, plate showing. 62 borders for. 57-68 cultural features on. 52-53 enlargement and reduction of. 18 explanations for. 19, 58-59 geologic, details of, plate showing. 58 printing of. 87-89 standard colors for. 62-63 hydrographic features on. 61-52 lettering on. 53-65 materials used for drawing. 23-28 orientation of. 18 original, margin required on. 19 original base, amount of detail on. 17 must be free from colors and symbols. 28 preparation of. 13-14, 17-18 original geologic, method of coloring. 27-28 projection for. 18-19, 43-45 reduction or enlargement of, marking for. 63-64 relief on. 48-51 standard scales for. 18 symbols used on. 20-23 drawing of. 61 plates showing. 20, 46 titles for. 58 topographic, scales of. 14-15 Mathematical signs, forms and names of. 94 Measures, linear, metric equivalents of. 92 Measuring scales for map projection, use of. 44 Meridians used on public-land maps, diagram showing. 16 Metric measures, English equivalents of. 92 Millionth-scale map, use of. 14 Mine plans, conventional lines for. 29 features of. 65-66 symbols used on, plate showing. 20 Minerals. _See_ Rocks. Mississippi River Commission, maps published by 15

N.

Names of rocks. 94-97 National forest maps and proclamations, use of. 15

O.

Offset process, description of. 87 Oilwells, symbols for. 21 Opaquing, meaning of. 18, 47, 86 Orientation of maps, requirements for. 18 Original drawings, general treatment of, by draftsmen. 42-43 preparation of. 12-40 Outdoor sketches, redrawing of. 69-70

P.

Panoramas, construction of. 71 Paper, kinds used for drawings. 23-24, 60, 61, 66, 69 Pastes, use of. 37 Patterns, areal, method of drawing. 61-62 areal, plate showing. 62 Pen drawings, materials and methods used in making. 67-68, 68-69 Pencils, colored, use of. 26 drawing, quality and grades of. 25, 66 Pens, kinds of, used for drawing. 25, 48, 67 Photoengraving, cost of. 75, 78, 80, 81 general features of. 72-73 Photoengravings, printing and insertion of. 11 Photogelatin processes, description of. 82-83 Photographs, adaptation of. 83 bleaching of. 69 care needed in taking and handling. 32, 33, 39-40 copyrighted, consent for use of. 33-34 duplicate prints of, requests for. 34 mounting and numbering of. 33, 36-37 poor, mating of drawings over. 68-69 preparation of, for half-tone engraving. 77-78 record of source of. 34 selection of. 32-33 retouching of. 68, 70-71 suitability of. 9 unpublished, issue and use of. 34 Photolithographs, changes in. 39 Photolithography, description of. 86-87 Planographic process, description of. 87 Plans of mines, drawing and lettering of. 29, 65-66 symbols used on, plate showing. 20 Plates, differences from figures. 10-11 divisions of, serial letters and numbers for. 12 grouping small illustrations on. 36-37 methods of inserting, plate showing. 12 Political divisions, lettering of. 53, 54 Post-route maps, scales and detail of. 15 Projection for maps, preparation and checking of. 18-19, 43-45 Proofs, changes in. 76 correction of. 38-39 duplicate, supplying of. 30 submittal of. 38 Public-land maps, meridians, parallels, and township lines used on, diagram showing. 16 Public works, lettering of. 53 Punctuation marks, forms of. 54 Purpose of illustrations in Survey reports. 8, 40

R.

Railroad surveys, data for maps obtainable from. 15 Railroads, names of, on maps. 57 Reduction of maps, marking drawings for. 63-64 means of. 18 Reduction sheet for lettering, plate showing. 54 use of. 55 Relief, methods of expressing. 48-51 Reproduction of illustrations, processes for. 72-90 relation of, to the drawing supplied. 7, 40 Reticulation, sketching by. 47 Retouching of photographs, materials and method used in. 68, 70-71 Reuse of illustrations, procedure for. 37-38 Rocks, igneous, names of. 95-97 metamorphic, names of. 95 sedimentary, names of. 94-95 symbols used to distinguish. 32 _See also_ Specimens. Roman numerals, numbers expressed by. 93 Rubber, liquid, use of. 37

S.

Scales, bar, forms of. 50-60 measuring for projection of maps. 44 standard, of maps. 18 Scope of this manual. 7 Screens, half-tone prints showing effects produced by. 56 Selection of illustrations, considerations governing. 8-9 Sections, columnar, original drawings for. 31 columnar, symbols used in, plate showing. 32 structure, combination of, with views of topography. 30-31 drawing of. 64-65 original drawings for. 29-31 symbols used in, plate showing. 32 vertical exaggeration of. 30 Shading, kinds used. 67 Signs, mathematical, forms and names of. 04 Sises of illustrations. 11-12, 40 Specimens, borrowed and fragile, care of. 35 drawings of, methods of making. 60-68 paleontologic, transmittal of. 35 photographs of, how printed. 68 how used. 34-85 Springs, symbols for. 22, 23 State maps, use of. 15 Stipple, production of. 50, 51 Stone, engraving on. 89-90 Streams, drawing of. 51-52 lettering names of. 52 Submittal of illustrations. 10 Symbols, drawing of. 20, 61 for ground-water features, uniformity needed in. 21-23 for maps and mine plans, plates showing. 20, 46 uniform use of. 20, 45-46 for oil and gas wells, features of. 21 for structure and columnar sections, plate showing. 32 lithologic, use of. 32

T.

Three-color half-tones, process of making. 78-80 Titles of illustrations, arrangement and place of. 58 printing of. 19-20 wording and lettering of. 19 Tooling on half-tones, effects obtained by. 77, 78 Topographic atlas sheets, scales of. 14 Tracing, method of. 46-47 use of colors in. 46-47 Tracing linen, use of. 24-25 Transferring, celluloid, process of. 47 celluloid, requisitions for. 47 Type, lettering with. 54-55 styles and sizes of. 55

V.

Value of illustrations in Survey reports. 8 Vara, length of. 92 Vignetting, effect obtained by. 78

W.

Wall map of the United States, use of, for basemaps. 14 Water colors, use of. 26, 67, 71 Waterlining, use of. 52 Wax engraving, process and advantages of. 80-81 Wells, symbols for. 22, 23 Wood engraving, process of. 81-82

Z.

Zinc etchings, changes in. 38-39 drawings for. 74 insertion of. 11 making and advantages of. 73-75

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Transcriber's Note

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