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