Chapter II: Part 2

The ledges show little definite stratification and very little dip. The topography of the conglomerate is inconspicuous and consists of a slightly rolling valley without particular features. It approaches nearer to the level of the present drainage than any other formation, and decay by solution has gone on to a very considerable extent. Where the draining streams have approached their baselevel, scarcely an outcrop of conglomerate is seen. Where the areas of conglomerate lie near faster falling streams, the irregular masses of unweathered rocks appear.

When but slightly weathered the conglomerate forms an effective decorative stone and has been extensively used as a marble with the name "Potomac marble," from the quarries on the Potomac east of Point of Rocks, Maryland. While it is in no sense a marble, yet the different reds and browns produced by unequal weathering of the limestone pebbles have a very beautiful effect.

The thickness of the Newark formation is most uncertain. The rocks dip at a light angle to the west with hardly an exception, and the sections all appear to be continuous. Even with liberal deductions for frequent faults, nothing less than 3,000 feet will account for the observed areas and dips.

_Newark Diabase._

Description of the lithified deposits would be far from complete without reference to the later diabase which is associated with the Newark rocks.

These diabases, as they will be called generically, are usually composed of plagioclase feldspar, and diallage or augite; additional and rarer minerals are quartz, olivine, hypersthene, magnetite, ilmenite, and hornblende. Their structure is ophitic in the finer varieties, and to some extent in the coarser kinds as well. They are holocrystalline in form and true glassy bases are rare, rendering the term diabase more appropriate than basalt.

There is greater variety in texture, from fine aphanitic traps up to coarse grained dolerites with feldspars one-third of an inch long. The coarser varieties are easily quarried and are often used for building stone under the name of granite.

These forms are retained to the present day with no material change except that of immediate weathering, but to alterations of this kind they are an easy prey, and yield the most characteristic forms. The narrow dikes produce ridges between slight valleys of sandstone or shale, the wide bodies produce broad flat hills or uplands. The rock weathers into a fine gray and brown clay with numerous bowlders of unaltered rock of a marked concentric shape.

While the diabase dikes are most prominent in the Newark rocks, they are also found occasionally in the other terraces. In the Catoctin Belt they appear irregularly in the granite and schist. Rare cases also occur in the rocks of the Piedmont plain. The diabase of the Newark areas is almost exclusively confined to the red sandstone, and the dike at Leesburg cutting the limestone conglomerate is almost the only occurrence of that combination.

The diabase occurs only as an intrusive rock in the vicinity of the Catoctin Belt. Of this form of occurrence, however, there are two types, dikes and massive sheets or masses. The dikes are parallel to the strike of the inclosing sandstone as a rule, and appear to have their courses controlled by it on account of their small bulk. The large masses break at random across the sandstone in the most eccentric fashion. No dislocation can be detected in the sandstones, either in strike or dip, yet of course it must exist by at least the thickness of the intrusive mass. That this thickness is considerable is shown by the coarseness of the larger trap masses, which could occur only in bodies of considerable size, and also by the width of their outcrops in the westward dipping sandstones. The chief mass in point of size is three miles wide. This mass fast decreases in width as it goes north, without losing much of its coarseness, and ends in Leesburg in a hooked curve. The outline of the diabase is suggestive of the flexed trap sheets of more northern regions, but this appearance is deceptive, since the diabase breaks directly across both red sandstone and limestone conglomerate, which have a constant north and south strike. An eastern branch of this mass crosses the Potomac as a small dike and passes north into Pennsylvania. The diabase dikes in the Catoctin Belt are always narrow, and, while many outcrops occur along a given line, it is probable that they are not continuous.

At Leesburg the limestone conglomerate next the diabase is indurated, its iron oxide is driven off, and the limestone partly crystallized into marble.

_Catoctin Schist._

The Catoctin schist is geographically the most important of the volcanic rocks of Loudoun.

Throughout its entire area the schist is singularly uniform in appearance, so that only two divisions can be made with any certainty at all. These are dependent upon a secondary characteristic, viz, the presence of epidote in large or small quantities. The epidote occurs in the form of lenses arranged parallel to the planes of schistosity, reaching as high as five feet in thickness and grading from that down to the size of minute grains. Accompanying this lenticular epidote is a large development of quartz in lenses, which, however, do not attain quite such a size as those of epidote. Both the quartz and epidote are practically insoluble and lie scattered over the surface in blocks of all sizes. In places they form an almost complete carpet and protect the surface from removal. The resulting soil, where not too heavily encumbered with the epidote blocks, is rich and well adapted to farming, on account of the potash and calcium contained in the epidote and feldspar.

Except along the narrow canyons in the Tertiary baselevel the rock is rarely seen unless badly weathered. The light bluish green color of the fresh rock changes on exposure to a dull gray or yellow, and the massive ledges and slabs split up into thin schistose layers. It is quite compact in appearance, and as a rule very few macroscopic crystals can be seen in it.

A general separation can be made into an epidotic division characterized by an abundance of macroscopic epidote and a non-epidotic division with microscopic epidote. These divisions are accented by the general finer texture of the epidotic schist.

The schists can be definitely called volcanic in many cases, from macroscopic characters, such as the component minerals and basaltic arrangement. In most cases, the services of the microscope are necessary to determine their nature. Many varieties have lost all of their original character in the secondary schistosity. None the less, its origin as diabase can definitely be asserted of the whole mass. In view of the fact, however, that most of the formation has a well defined schistosity destroying its diabasic characters, and now is not a diabase but a schist, it seems advisable to speak of it as a schist.

Sections of the finer schist in polarized light show many small areas of quartz and plagioclase and numerous crystals of epidote, magnetite, and chlorite, the whole having a marked parallel arrangement. Only in the coarser varieties is the real nature of the rock apparent. In these the ophitic arrangement of the coarse feldspars is well defined, and in spite of their subsequent alteration the fragments retain the crystal outlines and polarize together. Additional minerals found in the coarse schists are calcite, ilmenite, skeleton oblivine, biotite, and hematite.

_Rocks of the Piedmont Plain._

The Piedmont plain, where it borders upon the Catoctin Belt, is composed in the main of the previously described Newark strata, red sandstone, and limestone conglomerate. East of the Newark areas lies a broad belt of old crystalline rocks, whose relations to the Catoctin Belt are unknown.

The rocks, in a transverse line, beginning a little to the east of Dranesville, in Fairfax County, and extending to the Catoctin Mountain, near Leesburg, occur in the following order, viz: Red sandstone, red shale, greenstone, trap, reddish slate, and conglomerate limestone.

Heavy dykes of trap rock extend across the lower end of the County, from near the mouth of Goose Creek to the Prince William line. "These, being intrusive rocks, have in some places displaced the shale and risen above it, while in other places a thin coat of shale remains above the trappean matter, but much altered and changed in character."[7] A large mass of trap rock presents itself boldly above the shale at the eastern abutment of the Broad Run bridge, on the Leesburg and Alexandria turnpike. Not far to the east the shale is changed to a black or blackish brown color, while at the foot of the next hill still farther eastward the red shale appears unchanged. The summits of many of these dykes are "covered with a whitish or yellowish compact shale, highly indurated and changed into a rock very difficult to decompose."[8]

[Footnote 7: Taylor's _Memoir_.]

[Footnote 8: Ibid.]

_Lafayette Formation._

A great class of variations due to rock character are those of surface form. The rocks have been exposed to the action of erosion during many epochs, and have yielded differently according to their natures. Different stages in the process of erosion can be distinguished and to some extent correlated with the time scale of the rocks in other regions. One such stage is particularly manifest in the Catoctin Belt and furnishes the datum by which to place other stages. It is also best adapted for study, because it is connected directly with the usual time scale by its associated deposits. This stage is the Tertiary baselevel, and the deposit is the Lafayette formation, a deposit of coarse gravel and sand lying horizontally upon the edges of the hard rocks. Over the Coastal plain and the eastern part of the Piedmont plain it is conspicuously developed, and composes a large proportion of their surfaces. As the formation is followed westward it is more and more dissected by erosion and finally removed. Near the area of the Catoctin Belt it occurs in several places, all of them being small in area. One is three miles northeast of Aldie. Here, a Newark sandstone hill is capped with gravel. This gravel is much disturbed by recent erosion and consists rather of scattered fragments than of a bedded deposit.

The materials of the Lafayette gravel are chiefly pebbles and grains of quartz, with a considerable admixture of quartzite and sandstone. The large quartz pebbles were probably derived from the large lenses of quartz in the Catoctin schist, for no other formation above water at the time contained quartz in large enough masses to furnish such pebbles. On the hypothesis that they were of local origin and merely worked over during submergence, they might be connected with the quartz veins of the Piedmont plain. That theory, however, with difficulty accounts for their well-rounded condition, which shows either beach action or long carriage. The quartz sand may well have been derived from the granitic quartzes, but that is an uncertain matter. The sandstones and quartzites are usually massive and pure white, of the variety found along Catoctin and Bull Run mountains. Other varieties of sandstone--the blue-banded type, for instance--are derived from the Weverton sandstone on the Blue Ridge. The white sandstone pebbles in the terraces along Bull Run Mountain can be traced from the ledges to the deposits. In this region, therefore, an absolute shore can be seen. In other areas along Catoctin Mountain a shore can be inferred, because the mountain projects above the baselevel plane and contains no gravel deposits. In fact, only a few points at the stream gaps are cut down to the baselevel.

_Metamorphism._

Dynamic metamorphism has produced great rearrangement of the minerals along the eastern side of the Catoctin Belt, and results at times in complete obliteration of the characters of the granite. The first step in the change was the cracking of the quartz and feldspar crystals and development of muscovite and chlorite in the cracks. This was accompanied by a growth of muscovite and quartz in the unbroken feldspar. The aspect of the rock at this stage is that of a gneiss with rather indefinite banding. Further action reduced the rock to a collection of angular and rounded fragments of granite, quartz, and feldspar in a matrix of quartz and mica, the mica lapping around the fragments and rudely parallel to their surfaces. The last stage was complete pulverization of the fragments and elongation into lenses, the feldspathic material entirely recomposing into muscovite, chlorite, and quartz, and the whole mass receiving a strong schistosity, due to the arrangement of the mica plates parallel to the elongation. This final stage is macroscopically nothing more than a siliceous slate or schist, and is barely distinguishable from the end products of similar metamorphism in the more feldspathic schists and the Loudoun sandy slates. The different steps can readily be traced, however, both in the hand specimen and under the microscope.

The Weverton sandstone has suffered less from metamorphism than any of the sediments. In the Blue Ridge it has undergone no greater change than a slight elongation of its particles and development of a little mica. Along Catoctin Mountain, from the Potomac River south, however, increased alteration appears together with the diminution in thickness. What little feldspar there was is reduced to quartz and mica, and the quartz pebbles are drawn out into lenses. Deposition of secondary quartz becomes prominent, amounting in the latitude of Goose Creek to almost entire recrystallization of the mass. A marked schistosity accompanies this alteration, and most of the schistose planes are coated with silvery muscovite. Almost without exception these planes are parallel to the dip of the formation.

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.

In a great many places along the base of the mountain the formation of this type is somewhat complicated by the wash from the mountain, which consists principally of subangular quartz fragments, from 1 to 4 inches in diameter. This rock sometimes forms as much as 30 or 40 per cent of the soil mass. This phase is called "gravelly land," and is hard to cultivate on account of its heavy texture and stony condition, although it is inherently productive.

This type occurs in one irregular-shaped area, about 15 miles long, varying from less than 1 mile to 3 or 4 miles in width, being cut by the Potomac River just east of Point of Rocks, Md. It thus lies in the central part of the County, in the Piedmont Plateau, extending from immediately north of Leesburg, and skirting the eastern foot of Catoctin Mountain.

The general surface drainage is good, there being many small streams flowing through the type and emptying into the Potomac River. The stream beds are but little lower than the surface of the surrounding land, while the slopes are long and gentle. Excessive erosion scarcely ever occurs. The heavier phase of the type would undoubtedly be improved by tile draining, as it is usually lower lying than the lighter phase. The heavier phase bakes and cracks in dry weather much the same as the heavy limestone soils of the Shenandoah Valley, but with the lighter phases, where the soil covering is deeper, good tilth is easily maintained throughout the growing season.

Corn, wheat, clover, and grass are the crops grown, of which the yields are as follows: Corn, from 40 to 60 bushels per acre; wheat, from 15 to 25 bushels per acre, and clover and grass, from 1-1/2 to 2-1/2 tons of hay per acre.

The Penn clay is the most highly prized soil of the Piedmont region of Loudoun and brings the highest prices.

_Penn Stony Loam._

The Penn stony loam consists of from 8 to 12 inches of a red or grayish heavy loam, somewhat silty, underlain by a heavier red loam. From 10 to 60 per cent of gray and brown fragments of Triassic sandstone, ranging from 1 to 6 inches in thickness, cover the surface of the soil. The color is in general the dark Indian-red of the other soils derived from Triassic sandstone, being particularly marked in the subsoil.

This type occurs in the southeastern part of Loudoun, on the Piedmont Plateau. It occupies three small areas whose total extent probably does not exceed two and one-half square miles. It is closely associated with the Penn loam and grades gradually into that type. The only great difference between the two is the presence of sandstone fragments in the Penn stony loam.

The topography varies from gently rolling to hilly and ridgy, with slopes that are sometimes rather steep. However, the surface is not so broken as to interfere with cultivation, and the slopes are usually gentle.

The type is well drained, the slopes allowing a rapid flow of water from the surface, while the soil water passes readily through the soil and subsoil. On the other hand, the texture is sufficiently heavy to prevent undue leaching and drought.

Little of the land is in cultivation, on account of its stony character, which makes cultivation difficult. Where unimproved it is covered with a heavy growth of chestnut, oak, and pine. The land is locally called "chestnut land." In a few small areas the larger stones have been removed and the land is cultivated, corn and wheat being the principal crops. The yield of corn ranges from 20 to 35 bushels and of wheat from 8 to 15 bushels per acre. Apples and small fruits and vegetables do well.

_Iredell Clay Loam._

The soil of the Iredell clay loam consists of from 6 to 18 inches of light loam, usually brown or gray, although sometimes of a yellowish color, with an average depth of about twelve inches. The subsoil consists of a heavy yellow to yellowish-brown waxy clay. This clay is cold and sour, almost impervious to moisture and air, and protects the underlying rock from decay to a great extent. Often the clay grades into the rotten rock at from 24 to 36 inches. In the poorly drained areas a few iron concretions occur on the surface. Numerous rounded diabase bowlders, varying in size from a few inches to several feet in diameter, are also scattered over the surface of the soil. Occasional slopes of the type have had the soil covering entirely removed by erosion, and here, where the clay appears on the surface, the soil is very poor. In other places, where the soil covering is quite deep, as from 12 to 18 inches, the type is fairly productive, and its productiveness is generally proportional to the depth of the soil.

The local name for the Iredell clay loam is "wax land," from the waxy nature of the subsoil, or "black-oak land," from the timber growth. A few small, isolated areas of this soil occur in the intermediate valley of the Catoctin Belt, and here the texture is much the same as that described above; but the soil usually consists of from 6 to 10 inches of a drab or brown loam, underlain by a heavy mottled yellow and drab silty clay. This phase has few stones on the surface or in the soil. The local names for this phase are "cold, sour land" and "white clay."

The greater part of the Iredell clay loam occurs in the southern or southeastern corner of the County and occupies one large, irregular-shaped but generally connected area, extending from Leesburg, in a southeasterly and southerly direction along Goose Creek to the southern boundary of the County, the most typical development of the soil being at Waxpool. The phase already described occurs in small, disconnected areas, usually quite far apart, the general relative direction of these areas being northeast and southwest. They all lie in the intermediate valley of the Catoctin Belt, and are usually near the foot of the Blue Ridge or Short Hills. The most typical development of this phase occurs just southeast of Bluemont.

Where rolling and sloping the surface drainage is good, the water passing rapidly from the surface into the numerous small streams flowing into Goose Creek, which is the main drainage way of this type. In the low, flat lands the water stands or flows very slowly from the surface. Owing to the impervious nature of the clay subsoil, underdrainage is very slow, and the land is often cold and sour.

Corn, wheat, and grass are the principal crops grown on this soil type, the average yields per acre being as follows: Corn, from 20 to 40 bushels; wheat, from 8 to 15 bushels; and grass, from 1-1/2 to 2-1/2 tons. Apples do fairly well.

The greater part of the type is tilled, while the uncultivated areas are used for pasturage and wood lots, the forest growth being black oak. In dry seasons, where the soil covering is not deep, the land bakes and cracks, and in this condition it can not be cultivated. In wet seasons the soil becomes too wet and sticky to work.

_Penn Loam._

The Penn loam consists of from 8 to 12 inches of a dark, Indian-red loam, underlain by a heavier loam of the same color. This peculiar red color is distinctive of the formation wherever found, and, consequently, the type is one easily recognized. The texture of the type is very uniform, with the exception of a few small areas where the subsoil is a clay loam. The soil is locally termed "red-rock land," on account of the numerous small red sandstone fragments which occur in the soil and subsoil in quantities varying from 5 to 20 per cent of the soil mass. The soil is free from large stones or other obstructions to cultivation.

This type occurs in several large, irregular areas on the Newark formation of the Piedmont Plateau in the eastern part of the County. The areas have a general northeast and southwest trend. A few small areas occur in close proximity to the larger ones. One of the larger areas is situated just south of Leesburg, while another occurs east of Lucketts.

The topography consists of a gently rolling to nearly level plain, and there are no steep slopes or rough areas. Drainage in this type is excellent, the easy slopes allowing a gradual flow of water from the surface without undue erosion, except with very heavy rains on the steeper slopes. The loamy subsoil allows a ready but not too rapid percolation of surplus soil moisture, and never gets soggy or in a cold, sour condition. Numerous small streams extend throughout the area of this type, allowing a rapid removal of all surplus water into the Potomac River, the chief drainageway of the County. Along these streams, which in all cases have cut out beds some 10 to 30 feet below the surrounding plain, the slopes are gradual.

The original growth on the Penn loam was a forest of oak, hickory, and walnut, but at the present time nearly all of the type is cleared and farmed. The soil is not naturally very productive, but is prized on account of its great susceptibility to improvement, its quick responsiveness to fertilization, and its easy cultivation and management. The surface is smooth and regular, and the absence of stones, together with the loamy texture of the soil, makes it easy to maintain good tilth. Any addition of fertilizers or lime is immediately effective, and by judicious management the type may be kept in a high state of productiveness. Many fine farms with good buildings are to be seen on this type. The crops grown are corn, wheat, grass, clover, apples, and small fruits. Grazing, stock raising, and dairying are practiced to some extent. The land yields from 40 to 60 bushels of corn, from 10 to 15 or more bushels of wheat, and from 1 to 2 tons of hay per acre.

_Cecil Loam._

The soil of the Cecil loam consists of from 8 to 12 inches of a brown or yellow loam. The subsoil consists of a heavy yellow or red loam, or occasionally clay loam. The soil and subsoil are usually free from stones, but occasional areas have from 5 to 30 per cent of angular quartz or schist fragments on the surface. Often a mica-schist enters into the composition of the subsoil, giving it a soft and greasy feel.

The greater part of the intermediate valley or baselevel plain of the Catoctin Belt consists of the Cecil loam, and it occurs here as one large, connected area, inside of which are small areas of Cecil clay, Loudoun sandy loam, and Iredell clay loam. A considerable portion of the Catoctin Mountain also consists of the Cecil loam. In extent this is the most important soil type in Loudoun, covering about 33 per cent of the total area.

The Cecil loam, owing to its rolling character, is well drained throughout. Many small streams traverse it, affording ample outlets for surface water. The gently rolling areas are not generally subject to excessive erosion, but the steeper slopes wash badly, deep gullies and ditches being formed on the hillsides. Especially subject to erosion are the areas in which the subsoil contains a relatively large proportion of mica fragments. The soil and subsoil, though quite loamy, retain enough moisture in seasons of moderate rainfall to supply all growing crops.

The Cecil loam is devoted entirely to general farming. The crops grown are corn, wheat, grass, clover, vegetables, apples, and pears. The agricultural interests are further diversified by the practice of dairying and stock raising. The land is one of the best corn soils of Loudoun, being loamy and easily cultivated throughout the growing season. The average yield per acre ranges from 40 to 60 bushels. Wheat does very well, producing from 12 to 20 bushels per acre, and more in favorable seasons. Grass and clover yield at the rate of from 1 to 2 tons of hay per acre and form good grazing during a considerable part of the year. Apples and pears are grown everywhere on the type, usually in small orchards, and good yields of these fruits are obtained. Oats were at one time grown, and can be produced at the rate of from 35 to 50 bushels per acre, but the present acreage is small, the farmers claiming that this crop rapidly reduces the productiveness of the soil.

Nearly all of the type is in cultivated crops or pasture. The original timber growth was oak, hickory, and walnut; but little of this stands now, except on occasional woodlots. The Cecil loam is a soil which with careful treatment makes a fine farming land; but carelessly managed it very quickly deteriorates.

_Cecil Clay._

The soil of the Cecil clay consists of a heavy loam, red or brown in color, and having an average depth of 8 inches. The subsoil generally consists of a red clay, although it is sometimes a heavy clay loam. The surface is generally free from stones, though occasional small areas have a few quartz and granite or schist fragments. In the Piedmont areas small rounded diabase fragments occur on the surface. Occasionally on steep slopes or high knobs the soil covering has been washed away, leaving the heavy red clay exposed on the surface. These areas, however, are small.

The type occurs principally in the intermediate valley of the Catoctin Belt, between the Blue Ridge and the Catoctin Mountain, and on the west slopes of the Catoctin Mountain. In the valley it occupies several small, disconnected areas scattered throughout this region, while on the west slope of the mountain it is found in one of two long, broad areas, extending in a northeast and southwest direction. Three small areas occur near the southeastern corner of the County, and the type is here closely related to the Iredell clay loam.

The most typical areas of this soil occur in the Piedmont Plateau and on the gentle slopes at the foot of the Blue Ridge in the vicinity of Bluemont.

This soil type has excellent surface drainage and is well watered and drained throughout by small streams. Few of the slopes are so steep as to wash badly. The heavy clay subsoil retains ample moisture for plant growth and the soil is rarely so wet as to necessitate tile draining, although this would undoubtedly be very beneficial in the case of the heavier phases.

The whole of this soil is under cultivation and it is highly esteemed wherever found, being naturally a strong soil and susceptible of improvement. The original forest growth consisted of oak, hickory, and walnut. The land is easily improved, retentive of moisture and manure, and with careful management makes an excellent soil for general farming. Owing to its tendency to bake, crops are liable to suffer during drought.

The land produces wheat, corn, grass, clover, apples, and pears. It is a strong wheat soil, and yields from 15 to 25 bushels per acre and occasionally more. Grass and clover hay yield at the rate of 1-1/2 to 2-1/2 tons per acre, while from 40 to 60 bushels of corn per acre are usually produced in good seasons.

All things considered, the Cecil clay is best adapted to the production of wheat and grass. The more loamy phases are adapted to corn, but the type as a whole is a much better wheat land than corn land. The soil is also well adapted to apples and pears. Bluegrass grows well and makes fine pasturage, and stock raising and dairy farming are other industries to which the Cecil clay is well suited. Care has to be used in the cultivation of this soil, for if worked when too wet it dries in large, hard clods that give trouble throughout the season and interfere with cultivation for a long time afterwards.

_Cecil Silt Loam._

The surface soil of the Cecil silt loam consists of 12 inches of a light gray or white silt loam. This material is underlain by a subsoil of yellow silt loam slightly heavier than the soil. The type is locally termed "white land," and is closely related to the Penn loam and the Iredell clay loam, these types surrounding and grading gradually into it. In some areas the soil is quite free from stones, while in others from 10 to 30 per cent of the soil mass is composed of small rock fragments.