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.