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_.]