Chapter 2

A third range, called "Catoctin Mountain," has its inception in Pennsylvania, traverses Maryland, is interrupted by the Potomac, reappears in Virginia at the river margin, opposite Point of Rocks, and extends through Loudoun County for a distance of twenty or more miles, when it is again interrupted.

Elevations on Catoctin Mountain progressively diminish southward from the Potomac River to Aldie, although the rocks remain the same, and the Tertiary drainage, which might be supposed to determine their elevations, becomes less effective in that direction.

Probably this mountain does not exceed an average of more than 300 feet above the surrounding country, though at some stages it may attain an altitude of 700 feet. Rising near the Potomac into one of its highest peaks, in the same range it becomes alternately depressed and elevated, until reaching the point of its divergence in the neighborhood of Waterford. There it assumes the appearance of an elevated and hilly region, deeply indented by the myriad streams that rise in its bosom.

On reaching the Leesburg and Snicker's Gap Turnpike road, a distance of twelve miles, it expands to three miles in width and continues much the same until broken by Goose Creek and its tributary, the North Fork, when it gradually loses itself in the hills of Goose Creek and Little River, before reaching the Ashby's Gap Turnpike.

The Catoctin range throughout Loudoun pursues a course parallel to the Blue Ridge, the two forming an intermediate valley or baselevel plain, ranging in width from 8 to 12 miles, and in altitude from 350 to 730 feet above sea level. Allusion to the physiography of this valley--so called only by reason of its relation to the mountains on either side--has been made elsewhere in this department.

Immediately south of Aldie, on Little River, near the point of interruption of Catoctin Mountain, another range commences and extends into Fauquier County. It is known as "Bull Run Mountain," but might rightly be considered an indirect continuation of the elevation of the Catoctin, its course and some of its features corresponding very nearly with that mountain save only that it is higher than any of the ranges of the latter, excepting the western.

East of the Catoctin the tumultuous continuity of mountains subsides into gentle undulations, an almost unbroken succession of sloping elevations and depressions presenting an as yet unimpaired variety and charm of landscape. However, on the extreme eastern edge of this section, level stretches of considerable extent are a conspicuous feature of the topography.

Three or four detached hills, rising to an elevation of 150 or 200 feet above the adjacent country, are the only ones of consequence met with in this section.

COMPARATIVE ALTITUDES.

The hilly character of Loudoun is clearly shown by the following exhibit of the elevation of points and places above tide-water. The variations of altitude noted in this schedule are based upon conflicting estimates and distinct measurements made at two or more points within a given circumference and slightly removed one from the other.

Feet. Sterling 415 Ashburn 320 Leesburg 321 to 337 Clarke's Gap 578 to 634 Hamilton 454 to 521 Purcellville 546 to 553 Round Hill 558 Bluemont 680 to 730 Snicker's Gap 1,085 Neersville 626 Hillsborough 550 Waterford 360 Mount Gilead 600 Oatlands 270 Little River, near Aldie 299 Middleburg 480 Potomac River, near Seneca Dam 188 Potomac River, at Point of Rocks 200 Potomac River, at Harper's Ferry 246

The whole of the county east of the Catoctin Mountain varies from 200 to 350 feet. The eastern base of the Blue Ridge has an elevation of about 730 feet, and the highest peak of that range in Loudoun rises 1,600 feet above tide-water.

The Short Hills have an approximate altitude of 1,000 feet, while that of the Catoctin Mountain varies from 300 to 700 feet. The valley between the Blue Ridge and Catoctin Mountains varies from 350 to 730 feet in elevation.

From many vantage points along the Blue Ridge may be obtained magnificent views of both the Loudoun and Shenandoah valleys. The eye travels entirely across the fertile expanse of the latter to where, in the far distance, the Alleghany and North Mountains rear their wooded crests. A few of the summits offer even more extensive prospects. From some nearly all of Loudoun, with a considerable area of Fairfax and Fauquier, is in full view. Other more distant areas within visionary range are portions of Prince William, Rappahannock, and Culpeper counties, in Virginia, Frederick and Montgomery counties, in Maryland, and even some of Prince George County, east of Washington City. Westward, the view embraces Shenandoah, Frederick, Clarke and Warren counties, in Virginia, Berkeley and Jefferson counties, in West Virginia, Washington County, in Maryland, and some of the mountain summits of Pennsylvania.

DRAINAGE.

The drainage of Loudoun can be divided into two provinces. One is the Potomac province, which is drained by a system of small tributaries of that stream. Its elevations are quite uniform and are referable to that master stream, whose grade is largely determined by its great basin beyond the "Catoctin belt." The second province is the region drained by smaller streams, chief of which is Goose Creek. In this province the drainage lines head entirely within the "Catoctin belt," and the elevations are variable according to the constitution of the rocks in the belt itself.

The tributaries by which the drainage of the two provinces is effected are Catoctin Creek, North Fork Catoctin Creek, South Fork Catoctin Creek, Little River, North Fork Goose Creek, Beaver-dam Creek, Piney Run, Jeffries Branch, Cromwells Run, Hungry Run, Bull Run, Sycoline Creek, Tuscarora Creek, Horse Pen Run, Broad Run, Sugarland Run, Elk Lick, Limestone Branch, and as many lesser streams.

The general slope of the county being to the northeast, the waters, for the most part, naturally follow the same course, as may be readily perceived by reference to maps of the section. The streams that rise in the Blue Ridge mostly flow to the eastward until they approach the Catoctin Mountain, where they are then deflected more toward either the north or south to pass that range by the Northwest Fork and Goose Creek, or by the Catoctin Creek which falls into the Potomac above Point of Rocks. East of Catoctin Mountain the streams pursue a more or less direct northern course.

Goose Creek, a right-hand branch of the Potomac River, is a considerable stream, pursuing a course of about fifty miles from its source in Fauquier County to its junction with the Potomac four miles northeast of Leesburg. It once bore the Indian name _Gohongarestaw_, meaning "River of Swans." Flowing northeastward across Loudoun, it receives many smaller streams until passing the first range of Catoctin Mountain, when it claims a larger tributary, the North Fork. Goose Creek represents subsequent drainage dependent on the syncline of the Blue Ridge and dating back at least as far as Cretaceous time. Its length in Loudoun is about thirty miles, and it has a fall of one hundred feet in the last twenty-two miles of its course. It drains nearly one-half the county and is about sixty yards wide at its mouth.

Catoctin Creek is very crooked; its basin does not exceed twelve miles as the crow flies, and includes the whole width of the valley between the mountains except a small portion in the northeastern angle of the County. Yet its entire course, measuring its meanders, would exceed thirty-five miles. It has a fall of one hundred and eighty feet in the last eighteen miles of its course, and is about twenty yards wide near its mouth.

The Northwest Fork rises in the Blue Ridge and flows southeastward, mingling its waters with the Beaver Dam, coming from the southwest, immediately above Catoctin Mountain, where their united waters pass through a narrow valley to Goose Creek.

Little River, a small affluent of Goose Creek, rises in Fauquier County west of Bull Run mountain and enters Loudon a few miles southwestward of Aldie. It pursues a northern and northeastern course until it has passed that town, turning then more to the northward and falling into Goose Creek. Before the Civil War it was rendered navigable from its mouth to Aldie by means of dams.

Broad Run, the next stream of consequence east of Goose Creek, rises in Prince William County and pursues a northern course, with some meanderings through Loudoun. It flows into the Potomac about four miles below the mouth of Goose Creek.

Sugarland Run, a still smaller stream, rises partly in Loudoun, though its course is chiefly through Fairfax County, and empties into the Potomac at the northeastern angle of the County.

In its southeastern angle several streams rise and pursue a southern and southeastern course, and constitute some of the upper branches of Occoquan River.

Perhaps no county in the State is better watered for all purposes, except manufacturing in times of drought. Many of the farms might be divided into fields of ten acres each and, in ordinary seasons, would have water in each of them.

There are several mineral springs in the county of the class called chalybeate, some of which contain valuable medicinal properties, and other springs and wells that are affected with lime. Indeed, in almost every part of the County, there is an exhaustless supply of the purest spring water. This is due, in great part, to the porosity of the soil which allows the water to pass freely into the earth, and the slaty character of the rocks which favors its descent into the bowels of the hills, from whence it finds its way to the surface, at their base, in numberless small springs. The purity of these waters is borrowed from the silicious quality of the soil.

The largest spring of any class in the county is Big Spring, a comparatively broad expanse of water of unsurpassed quality, bordering the Leesburg and Point of Rocks turnpike, about two miles north of Leesburg.

The springs, as has been stated, are generally small and very numerous, and many of them are unfailing, though liable to be affected by drought. In such cases, by absorption and evaporation, the small streams are frequently exhausted before uniting and often render the larger ones too light for manufacturing purposes. Nevertheless, water power is abundant; the county's diversified elevation giving considerable fall to its water courses, and many sites are occupied.

CLIMATE.

Because responsible statistical data is usually accorded unqualified credence, it is without undue hesitation that the following bit of astonishing information, gleaned from a reliable source, is here set down as positive proof of the excellence of Loudoun's climate: "It (Leesburg) is located in a section the healthiest in the world, as proven by statistics which place the death rate at 8-1/2 per 1,000, the very lowest in the table of mortality gathered from all parts of the habitable globe."

The climate of Loudoun, like that of most other localities, is governed mainly by the direction of the prevailing winds, and, to a limited extent, is influenced by the county's diversified physical features.

Though the rainfall is abundant, amounting annually to forty or fifty inches, ordinarily the air is dry and salubrious. This ample precipitation is usually well distributed throughout the growing season and is rarely insufficient or excessive. The summer rainfall comes largely in the form of local showers, scarcely ever attended by hail. Loudoun streams for the most part are pure and rapid, and there appears to be no local cause to generate malaria.

In common with the rest of Virginia the climate of Loudoun corresponds very nearly with that of Cashmere and the best parts of China. The mean annual temperature is 50° to 55°.

Loudoun winters are not of long duration and are seldom marked by protracted severity. Snow does not cover the ground for any considerable period and the number of bright sunny days during these seasons is unusually large. In their extremes of cold they are less rigorous than the average winters of sections farther north or even of western localities of the same latitude. Consequently the growing season here is much more extended than in either of those sections. The prevailing winds in winter are from the north and west, and from these the mountains afford partial protection.

The seasons are somewhat earlier even than in the Shenandoah Valley, just over the western border of Loudoun, and the farmers here plant and harvest their crops from one week to ten days earlier than the farmers of that region.

Loudoun summers, as a rule, are long and agreeably cool, while occasional periods of extreme heat are not more oppressive than in many portions of the North. The mountains of Loudoun have a delightful summer climate coupled with inspiring scenery, and are well known as the resort of hundreds seeking rest, recreation, or the restoration of health. This region, owing to its low humidity, has little dew at night, and accordingly has been found especially beneficial for consumptives and those afflicted with pulmonary diseases. The genial southwest trade winds, blowing through the long parallel valleys, impart to them and the enclosing mountains moisture borne from the far away Gulf of Mexico.

GEOLOGY.

The geology of more than half the area of Loudoun County has received thorough and intelligent treatment at the hands of Arthur Keith in his most excellent work entitled "_Geology of the Catoctin Belt_," authorized and published by the United States Geological Survey.[5]

[Footnote 5: Credit for many important disclosures and much of the detail appearing in this department is unreservedly accorded Mr. Keith and his assistants.]

Mr. Keith's analysis covered the whole of Bull Run Mountain, the Catoctin in its course through Virginia and Maryland to its termination in southern Pennsylvania, the Blue Ridge and South Mountain for a corresponding distance, all intermediate ridges and valleys and contiguous territory lying outside this zone and paralleling the two flanking ranges.[6]

[Footnote 6: The name "Catoctin Belt" is applied to this region because it is separated by Catoctin Mountain from the Piedmont plain as a geographic unit more distinctly than in any other area, and because its geological unity is completed by Catoctin more fully and compactly than elsewhere.]

In this important work the Catoctin Belt is shown to be an epitome of the leading events of geologic history in the Appalachian region. It contains the earliest formations whose original character can be certified; it contains almost the latest known formations; and the record is unusually full, with the exception of the later Paleozoic rocks. Its structures embrace nearly every known type of deformation. It furnishes examples of every process of erosion, of topography derived from rocks of nearly every variety of composition, and of topography derived from all types of structure except the flat plateau type. In the recurrence of its main geographic features from pre-Cambrian time till the present day it furnishes a remarkable and unique example of the permanence of continental form.

With certain qualifications, a summary of the leading events that have left their impress on the region is as follows:

1. Surface eruption of diabase.

2. Injection of granite.

3. Erosion.

4. Surface eruption of quartz-porphyry, rhyolite, and andesite.

5. Surface eruption of diabase.

6. Erosion.

7. Submergence, deposition of Cambrian formations; slight oscillations during their deposition; reduction of land to baselevel.

8. Eastward tilting and deposition of Martinsburg shale; oscillations during later Paleozoic time.

9. Uplift, post-Carboniferous deformation and erosion.

10. Depression and Newark deposition; diabase intrusion.

11. Uplift, Newark deformation; and erosion to Catoctin baselevel.

12. Depression and deposition of Potomac, Magothy, and Severn.

13. Uplift southwestward and erosion to baselevel.

14. Uplift, warping and degradation to Tertiary baselevel; deposition of Pamunkey and Chesapeake.

15. Depression and deposition of Lafayette.

16. Uplift and erosion to lower Tertiary baselevel.

17. Uplift, warping and erosion to Pleistocene baselevel; deposition of high-level Columbia.

18. Uplift and erosion to lower Pleistocene baselevel; deposition of low-level Columbia.

19. Uplift and present erosion.

Along the Coastal plain reduction to baselevel was followed by depression and deposition of Lafayette gravels; elevation followed and erosion of minor baselevels; second depression followed and deposition of Columbia gravels; again comes elevation and excavation of narrow valleys; then depression and deposition of low-level Columbia; last, elevation and channeling, which is proceeding at present. Along the Catoctin Belt denudation to baselevel was followed by depression and deposition of gravels; elevation followed and erosion of minor baselevels among the softer rocks; second depression followed, with possible gravel deposits; elevation came next with excavation of broad bottoms; last, elevation and channeling, at present in progress.

The general structure of the Catoctin Belt is anticlinal. On its core appear the oldest rocks; on its borders, those of medium age; and in adjacent provinces the younger rocks. In the location of its system of faulting, also, it faithfully follows the Appalachian law that faults lie upon the steep side of anticlines.

After the initial location of the folds along these lines, compression and deformation continued. Yielding took place in the different rocks according to their constitution.

Into this system of folds the drainage lines carved their way. On the anticlines were developed the chief streams, and the synclines were left till the last. The initial tendency to synclinal ridges was obviated in places by the weakness of the rocks situated in the synclines, but even then the tendency to retain elevation is apt to cause low ridges. The drainage of the belt as a whole is anticlinal to a marked degree, for the three main synclinal lines are lines of great elevation, and the anticlines are invariably valleys.

In order of solubility the rocks of the Catoctin Belt, within the limits of Loudoun County, to which section all subsequent geologic data will be confined, stand as follows:

1. Newark limestone conglomerate; calcareous.

2. Newark sandstone and shale; calcareous and feldspathic.

3. Newark diabase; feldspathic.

4. Granite; feldspathic.

5. Loudoun formation; feldspathic.

6. Granite and schist; feldspathic.

7. Catoctin schist; epidotic and feldspathic.

8. Weverton sandstone; siliceous.

All of these formations are in places reduced to baselevel. The first three invariably are, unless protected by a harder rock; the next three usually are; the Catoctin schist only in small parts of its area; the Weverton only along a small part of Catoctin Mountain.

The Catoctin Belt itself may be described as a broad area of igneous rocks bordered by two lines of Lower Cambrian sandstones and slates. Over the surface of the igneous rocks are scattered occasional outliers of the Lower Cambrian slate; but far the greater part of the surface of the belt is covered by the igneous rocks. The belt as a whole may be regarded as an anticline, the igneous rocks constituting the core, the Lower Cambrian the flanks, and the Silurian and Newark the adjoining zones. The outcrops of the Lower Cambrian rocks are in synclines, as a rule, and are complicated by many faults. The igneous rocks have also been much folded and crumpled, but on account of their lack of distinctive beds the details of folds can not well be traced among them.

They are the oldest rocks in the Catoctin Belt and occupy most of its area. They are also prominent from their unusual character and rarity.

An important class of rocks occurring in the Catoctin Belt is the sedimentary series. It is all included in the Cambrian period and consists of limestone, shale, sandstone and conglomerate. The two border zones of the Catoctin Belt, however, contain also rocks of the Silurian and Juratrias periods. In general, the sediments are sandy and calcareous in the Juratrias area, and sandy in the Catoctin Belt. They have been the theme of considerable literature, owing to their great extent and prominence in the topography.

_Granite._

The granite in the southern portion of the County is very important in point of extent, almost as much so as the diabase in the same section.

The areas of granite are, as a rule, long narrow belts, and vary greatly in width.

The mineralogical composition of the granite is quite constant over large areas. Six varieties can be distinguished, however, each with a considerable areal extent. The essential constituents are quartz, orthoclase and plagioclase, and by the addition to these of biotite, garnet, epidote, blue quartz, and hornblende, five types are formed. All these types are holocrystalline, and range in texture from coarse granite with augen an inch long down to a fine epidote granite with scarcely visible crystals.

_Loudoun Formation._

Among the various Cambrian formations of the Catoctin Belt there are wide differences in uniformity and composition. In none is it more manifest than in the first or Loudoun formation. This was theoretically to be expected, for first deposits upon a crystalline foundation represent great changes and transition periods of adjustment among new currents and sources of supply. The Loudoun formation, indeed, runs the whole gamut of sedimentary possibilities, and that within very short geographical limits. Five miles northwest of Aldie the Loudoun formation comprises limestone, slate, sandy slate, sandstone, and conglomerate with pebbles as large as hickory nuts. These amount in thickness to fully 800 feet, while less than three miles to the east the entire formation is represented by eight or ten feet of black slate.