Chapter 4

Metamorphism of the Loudoun formation is quite general. It commonly appears in the production of phyllites from the argillaceous members of the formation, but all of the fragmental varieties show some elongation and production of secondary mica. The limestone beds are often metamorphosed to marble, but only in the eastern belt. The recrystallization is not very extensive, and none of the marbles are coarse grained.

The metamorphism of the igneous rocks is regional in nature and has the same increase from west to east as the sediments.

In the granite it consists of various stages of change in form, attended by some chemical rearrangement. The process consisted of progressive fracture and reduction of the crystals of quartz and feldspar, and was facilitated by the frequent cleavage cracks of the large feldspars. It produced effects varying from granite with a rude gneissoid appearance, through a banded fine gneiss, into a fine quartz schist or slate. These slaty and gneissoid planes are seen to be parallel to the direction and attitude of the sediments, wherever they are near enough for comparison.

Dynamic alteration of the Catoctin diabase is pronounced and wide-spread. Macroscopically it is evident in the strong schistosity, which is parallel to the structural planes of the sediments when the two are in contact. In most areas this alteration is mainly chemical and has not affected the original proportions of the rock to a marked extent. Its prevalence is due to the unstable composition of the original minerals of the rock, such as olivine, hypersthene, and pyroxene. Along Catoctin Mountain, however, both chemical and mechanical deformation have taken place, so that the original rock structure is completely merged into pronounced schistosity. This was materially assisted by the weak lath shapes of the feldspar and the mobility of the micas.

The average dip of the schistose planes is about 60°; from this they vary up to 90° and down to 20°. In all cases they are closely parallel to the planes on which the sediments moved in adjustment to folding, namely, the bedding planes. In regions where no sediments occur, the relation of the schistose planes to the folds can not be discovered.

Parallel with the micas that cause the schistosity, the growth of the quartz and epidote lenses took place. These, too, have been deformed by crushing and stretching along Bull Run Mountain and the south part of Catoctin Mountain. From this fact, taken in connection with the folding of the schistose planes at Point of Rocks, it would appear that the deformation was not a single continuous effort.

The ratios of schistose deformation in the igneous rocks are as follows: diabase, with unstable mineral composition and small mechanical strength, has yielded to an extreme degree; granite, with stable composition and moderate mechanical strength, has yielded to the more pronounced compression.

MINERAL AND KINDRED DEPOSITS.

In point of mineral wealth Loudoun ranks with the foremost counties of the State. Iron, copper, silver, soapstone, asbestos, hydraulic limestone, barytes, and marble are some of the deposits that have been developed and worked with a greater or lesser degree of success.

A large bed of compact red oxide of iron lies at the eastern base of the Catoctin Mountain, on the margin of the Potomac River. Long before the Civil War a furnace was erected here by Samuel Clapham, Sr., for the reduction of this ore, and considerable quantities of it were formerly transported moderate distances to supply other furnaces. The Clapham furnace continued in operation until all the fuel at hand was consumed and then went out of blast. Water power was supplied by the Catoctin Creek, which flows into the river immediately above the mountain. To obtain this a tunnel was cut through a spur of the mountain projecting into a bend of the creek. This tunnel, about five hundred feet long and sixty feet beneath the summit of the hill, was cut through almost a solid wall of rock, and, at that day, was considered a great work.

Magnetic iron ore has been found in certain places, and this or a similar substance has a disturbing effect upon the needle of the surveyor's compass, rendering surveying extremely difficult where great accuracy is required. In some instances the needle has been drawn as much as seven degrees from its true course. This effect is more or less observable nearly throughout the Catoctin Mountain, and has been noted elsewhere in the County.

Chromate of iron was long ago discovered along Broad Run, and, about the same time, a bed of micaceous iron ore on Goose Creek below the Leesburg turnpike. Copper ore is associated with the last-named mineral.

In 1860, the output of pig iron in Loudoun was 2,250 tons, and its value $58,000. Rockbridge was the only Virginia County to exceed these figures.

In several localities small angular lumps of a yellowish substance, supposed to contain sulphur, have been found, embedded in rocks. When subjected to an intense heat, it gives forth a pungent sulphurous odor.

Small quantities of silver ore are discovered from time to time; but the leads have never been extensively worked and many of the richest veins are still untouched.

Deposits of copper in the schists have long excited interest and led to mining operations. The amount of ore, however, appears not to have justified any considerable work.

Near the base of the Catoctin Mountain, where it is first approached by Goose Creek, marble of an excellent quality is found but has been little worked. Among the varieties at the quarry are included pure white, white and pink, blue and white, white and green, serpentinized and chloritic serpentinized marble. These marbles are of great beauty and susceptible of a good polish. The calcareous bed here is about fifty feet thick and reaches southward for three miles with increasing thickness. At its southern end it is not entirely metamorphosed into marble, but retains its original character of fine blue limestone. Northward along this range the thickness of the marble constantly diminishes and rarely exceeds ten feet. Sometimes there are two beds, sometimes only one. At Taylorstown, just south of the Potomac, the bed is about three feet thick; on the north side of the Potomac about four or five feet. Here, as elsewhere, the beds of marble are inclosed in a bluish green micaceous schist, which has been thoroughly transformed by mechanical pressure.

In the vicinity of Leesburg and north of that town, and between the Catoctin Mountain and the Potomac River, the conglomerate limestone or brecciated marble is found in abundance, associated with red shale. It is a calcareous rock, apparently formed in part of pebbles cemented together and, when burned, produces an inferior lime. It is commonly known as Potomac marble. Of this variegated marble were formed the beautiful columns in the old Representatives' chamber of the Capitol at Washington. The soil in which this rock occurs is extremely productive and valuable.

The exhibition at the World's Fair, at New Orleans, of the following specimens of Loudoun minerals claimed much interest from visiting mineraloguists:

1. _Specular Iron Ore_, from near Leesburg, said to be in quantity. From Professor Fontaine.

2. _Chalcopyrite_, from near Leesburg, said to be a promising vein. From Professor Fontaine.

The following were contributed by the "Eagle Mining Company," of Leesburg; F. A. Wise, general manager:

1. _Carbonate of Copper_, from vein 3' wide, developed to 25' deep. Assays by Oxford Copper Company of New York give 51 per cent of copper and 27 ounces of silver per ton.

2. _Sulphuret of Copper_, from vein 10" wide, developed to 50' deep. Assays by Oxford Copper Company of New York give 12-1/2 per cent of copper.

3. _Iron Ore_, from vein 4' wide and 50' deep. Yields 55 per cent metallic iron by assay of W. P. Lawver, of U. S. Mint.

4. _Sulphuret of Copper_, from vein developed 50'. Yields 11 per cent of copper and 1 ounce of silver per ton by assay of W. P. Lawver, U. S. Mint.

5. _Carbonate of Copper_, red oxide and glance, from vein 3' wide, developed to 25' deep. Yields 50 per cent metallic copper and 27 ounces silver per ton by assays.

6. _Iron Ore_, from vein 2' to 4' wide, developed 50'. Yield 55 per cent metallic iron.

7. _Oxide of Copper_, from Carbonate vein, developed 60' on 4' wide vein; 25' deep.

8. _Sulphuret of Copper_, from vein 8" to 15" wide, developed 50'.

9. _Iron Ore._

10. _Barytes_, heavy spar, vein undeveloped.

11. _Iron Ore_, from 50' level of Eagle Mining Company's shaft.

12. _Marble_, from quarry of "Virginia Marble Company," three miles east from Middleburg. The deposit has been demonstrated to be of great extent; the marble has been pronounced of a very superior quality. Contributed by Major B. P. Noland.

13. _Marble_, from same as above.

14. " " " " "

* * * * *

17. _Copper Ore_, James Pinkham, from Virginia Department of Agriculture.

In the "_Handbook on the Minerals and Mineral Resources of Virginia_" prepared by the Virginia Commission to the St. Louis Exposition, Loudoun is credited with the three comparatively rare minerals given below. The two first-named occur nowhere else in the State.

"ACTINQLITE: _Calcium-magnesium-iron, Amphibole_,

Ca (Mg Fe)_{3}(Si O{4}){3}.

Specific Gravity, 3-3.2. Hardness, 5-6. Streak, uncolored.... Fine radiated olive-green crystals are found ... at Taylorstown...."

"TREMOLITE: _A variety of Amphibole. Calcium._

_Magnesium Amphibole._ Ca Mg{2}(Si O{4}){3}.

Specific Gravity, 2.9-3.1. Hardness, 5.6. Long bladed crystals; also columnar and fibrous. Color, white and grayish. Sometimes nearly transparent. Found in the greenish talcose rocks at Taylorstown."

_Chromite_, of which no occurrence of economic importance has yet been discovered in the County or elsewhere in Virginia.

"[9]On the eastern flank of the Catoctin rests a thin belt of mica slate. This rock is composed of quartz and mica in varying proportions, and this belt, on reaching the Bull Run Mountain, there expands itself, and forms the whole base of that mountain, and where the mica predominates, as it does there, it sometimes forms excellent flagging stones."

[Footnote 9: Taylor's _Memoir_.]

* * * * *

"Immediately at the western base of the Catoctin Mountain, a range of magnesian or talcose slates occur traversing its whole length.... In this range a vein of magnesian limestone is met with, and is exposed in several places. It however is narrow, in some places only a few feet in thickness, and being difficult to obtain is not much sought after for burning."

* * * * *

"Along the eastern side of the valley (Loudoun) gneiss is frequently met with on the surface, and where the larger streams have worn deep valleys, it is sometimes exposed in high and precipitous cliffs. This is more particularly the case along Goose Creek and Beaver Dam. Associated with it, however, is clay slate, not so much in rock as in soil, for it being more readily decomposed is seldom found on the surface, except as soil. These two varieties are often met with side by side in thin layers, and their combination at the surface forms a peculiarly favorable soil for agricultural purposes. The gneiss from the quartz it contains makes a sandy soil, while the clay slate gives it tenacity. This happy combination is a prevailing feature of this entire valley, and renders it one of the best farming sections in Virginia.

"Another rock that is a valuable acquisition is hornblende. This kind when first taken from the ground, is always covered as with a coat of rust. This is doubtless the fact, for the oxydasion of the iron it contains gives it that appearance, and colors the soil a reddish hue in its immediate vicinity. Wherever this rock abounds, the soil is durable and the crops are usually heavy. It is sometimes met with having a fine grain, and so very hard as to be almost brittle, though generally very difficult to break, and when broken strongly resembling cast-iron, and will sometimes ring, on being struck, almost as clearly. It was used very much formerly for making journals to run mill-gudgeons upon. When found on the surface, it is usually of a rounded form...."

However, much of the rock of the valley partakes of the nature of both hornblend and gneiss, and has been aptly termed a "hornblend gneiss rock."

Beds of magnesian or talcose slate, sometimes containing crystals of sulphuret of iron, are frequently met with in this section, and at the base of Black Oak Ridge, which is composed chiefly of chlorite slate and epidote, another bed of magnesian limestone is found. Containing about 40 per cent of magnesia, it makes an excellent cement for walls, but is of little or no value as a fertilizer.

SOILS.[10]

The soils of Loudoun vary greatly in both geological character and productiveness, every variety from a rich alluvial to an unproductive clay occurring within her boundaries. In general the soils are deep and rich and profitably cultivated.

The heavy clay soils of Loudoun are recognized as being the strongest wheat and grass soils. The more loamy soils are better for corn on account of the possibility of more thorough cultivation. However, the lands all have to be fertilized or limed to obtain the best results, and with this added expense the profit in wheat growing is extremely uncertain on any but the clay soils. The loamy soils are especially adapted to corn, stock raising, and dairying, and they are largely used for these purposes. The mountain sandstone soils, which are rough and stony, are not adapted to any form of agriculture; but for some lines of horticulture--as, for instance, the production of grapes, peaches, apples and chestnuts--or forestry they seem to offer excellent opportunities. The schist soil of the mountains, although rough and stony, is productive, easily worked, and especially adapted to apples, peaches, and potatoes. The shale and mica soils, although thin and leachy, are especially adapted to grapes, vegetables, and berries, and other small fruits. These soils should be managed very carefully to obtain the best results. They are easily worked and very quickly respond to fertilization and thorough cultivation. It is very probable that market gardening and fruit raising on these types would prove profitable. It seems, however, that peach trees are short lived on these soils. The meadow lands are low and subject to overflow, although otherwise well drained. They are best adapted to the production of corn, grass, and vegetables.

[Footnote 10: For the bulk of the information appearing under this caption the author is indebted to Carter's and Lyman's _Soil Survey of the Leesburg Area_, published in 1904 by the United States Department of Agriculture.]

That part of the County lying east of a line drawn from the Potomac River near Leesburg, by Aldie to the Fauquier line, is much more unproductive than the western portion, partly on account of an inferior soil, and partly in consequence of an exhausting system of cultivation, once so common in eastern Virginia, i. e., cropping with corn and tobacco without attempting to improve the quality of the soil. When impoverished, the lands were thrown out to the commons.

Large tracts that formerly produced from thirty to forty bushels of corn to the acre, still remain out of cultivation, though many of the present proprietors are turning their attention to the improvement of these soils and are being richly rewarded.

In this section, particularly along Goose Creek, trap-rock occurs, sometimes covering large surfaces, at other times partially covered with indurated shale, formed from the red shale of this region which has become hardened by the heat of the intruding trap. Where this rock occurs covering large surfaces, nearly level, "the soil is a dark brown colored clay, very retentive of moisture and better adapted to grass than grain.... A deficiency of lime probably occurs here, and there may be some obnoxious ingredient present. Minute grains of iron sand are generally interspersed through this rock, and as it is not acted upon by atmospheric influences, its combination may contain some acid prejudicial to vegetation. Where this rock is thrown into more irregular elevations, and is apparently more broken up, the soil is better."[11]

Near the Broad Run Bridge the soil is deplorably sterile. "In many places it is but a few inches in thickness, and the rock below, being compact, prevents the water from penetrating much below the surface, thus causing an excess of water in rainy weather, and a scarcity of it in fair weather. The red shale does not appear to decompose readily, as it is found a short distance beneath the surface, and the strata dipping at a low angle, prevents the water from freely descending into this kind of soil."[12]

[Footnote 11: Taylor's _Memoir_.]

[Footnote 12: Ibid.]

There is a huge belt of red land, known as "the red sandstone formation," extending from the Potomac through a part of each of the counties of _Loudoun_, Fairfax, Prince William, Fauquier, Culpeper, and Orange, which, with judicious cultivation, might be rendered liberally productive. Professor W. B. Rogers, in his report to the legislature of Virginia, in 1840, described it under the head of the "secondary formation in the northern district." "The general form of this area," he wrote, "is that of a prolonged triangle, extending in a direction from SSW. to NNE., having its apex at the southern extremity, and gradually expanding until it reaches the Potomac. Measured at a point on the Potomac between the mouths of Goose Creek and Broad Run, its length is about 80 miles. Its greatest breadth, as measured near the Potomac, and parallel to the road leading from Leesburg to Dranesville, is about 15 miles. This, in round numbers, gives 600 square miles for the area of this region."

Bottom lands of inexhaustible fertility and rich upland loams are commonly met with north and south of Leesburg for a considerable distance on either side of the turnpike leading from Point of Rocks, Md., at one extremity of the County to Middleburg at the other.

Limestone occurs in vast quantities throughout this zone, and there are present all the propitious elements that will be enumerated in the treatment of the soils of other areas.

The land here is in a high state of cultivation and, according to its peculiarly varying and unalterable adaptability, produces enormous crops of all the staple grains of the County.

The soil in the vicinity of Oatlands, included in this zone, is stiff and stony, except such as is adjacent to water courses, or the base of hills, where it is enriched by liberal supplies of decayed matter, which render it loamy and inexhaustible. In the main, it is of a generous quality, so pertinaciously retaining fertilizers as to withstand the washing of the heaviest rains. Still it is an anomaly that some of the richest areas in this region will not produce wheat; while, in the cultivation of rye, oats, and corn, satisfactory results are almost invariably obtained. Likewise there are but a few parcels whereon white clover does not grow spontaneously and in the greatest abundance. Than these, better pasture lands are found nowhere east of the Blue Ridge. Limestone occurs here in vast quantities.

In the Valley of Loudoun, between the Catoctin and Blue Ridge mountains, the soil is formed from gneiss, clay-slate, hornblend, greenstone, and quartz. The happy combination of these materials produces a most excellent and durable soil, containing, in fair proportions, alumina, silex, potash, lime, and other fertilizing minerals. Certain fertilizers have been successfully employed in improving its natural fertility, and when it is partially exhausted by excessive tillage, rest alone will restore it.

_Loudoun Sandy Loam._

The Loudoun sandy loam consists of from 8 to 12 inches of a heavy brown or gray sandy loam, underlain by a heavy yellow or red loam or clay loam. Often the subsoil contains a considerable quantity of coarse sand, making the texture much the same as that of the soil. The sand of the soil and subsoil is composed of very coarse rounded and subangular quartz particles. The surface material is not a light sandy loam, but is more like a loam containing considerable quantities of very coarse quartz fragments. It is generally quite free from stones, but small areas are occasionally covered with from 5 to 20 per cent of angular quartz fragments several inches in diameter.

The Loudoun sandy loam occurs in irregular areas of considerable size in the intermediate valley between the Blue Ridge, Short Hill, and Catoctin mountains. The largest area of the type is found in the vicinity of Round Hill.

The topography of this soil in the valley varies from gently rolling to hilly, the slopes being long and gently undulating, while along the valley walls and in the uplands it is ridgy. Owing to the position which this type occupies, surface drainage is good. The light texture of the soil admits of the easy percolation of water through it, and, except where the subsoil contains considerable sand, the soil moisture is well retained. In dry weather, if the ground is cultivated, a mulch is formed, which prevents the evaporation of the soil moisture and greatly assists the crops to withstand drought.

Nearly the whole of this type is in cultivation. Where the forest still stands the growth consists chiefly of oak. The soil is easy to handle, and can be worked without regard to moisture content. It is considered a good corn land, but is too light-textured for wheat, although a considerable acreage is devoted to this crop. Corn yields at the rate of 40 or 50 bushels per acre, wheat from 12 to 15 bushels and occasionally more, and grass and clover at the rate of 1 or 2 tons per acre. The productiveness of the soil depends greatly on the sand content of the subsoil. If the quantity be large, the soil is porous and requires considerable rain to produce good yields. If the clay content predominates, a moderate amount of rain suffices and good yields are obtained. Apples, pears, and small fruits do well on this soil.

_Penn Clay._

The Penn clay consists of from 6 to 12 inches of a red or reddish-brown loam, resting upon a subsoil of heavy red clay. The soil and subsoil generally have the Indian-red color characteristic of the Triassic red sandstone from which the soil is in part derived. From 1 to 10 per cent of the soil mass is usually made up of small sandstone fragments, while throughout the greater part of the type numerous limestone conglomerate ledges, interbedded with Triassic red sandstone, come to the surface. In other areas of the type numerous limestone conglomerate bowlders, often of great size, cover from 10 to 25 per cent of the surface.

This latter phase occurs in the vicinity of the Potomac River near Point of Rocks, Md., and near the Potomac, 3 miles north of Leesburg, and in these places the heavier phase of the type occurs, the clay often being very near the surface. In other parts of the County, where the limestone conglomerate is not so preponderant, or where it lies deeper and is mostly unexposed, the surface soil is deeper, often consisting of 18 inches of loam. The land is locally termed "limestone land." Near Catoctin Mountain the rocks seem to have weathered to considerable depth, there being no exposures or outcrops. Here the soil has been washed away from some of the more elevated small areas, and the heavy red clay subsoil is exposed.