History and Comprehensive Description of Loudoun County, Virginia. James William Head
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 8–½ 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]
[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]
[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