DRAINAGE.

The drainage of Loudoun can be divided into two provinces. One is the
Potomac province, which is drained by a system of small tributaries of
that stream. Its elevations are quite uniform and are referable to
that master stream, whose grade is largely determined by its great
basin beyond the "Catoctin belt." The second province is the region
drained by smaller streams, chief of which is Goose Creek. In this
province the drainage lines head entirely within the "Catoctin belt,"
and the elevations are variable according to the constitution of the
rocks in the belt itself.

The tributaries by which the drainage of the two provinces is effected
are Catoctin Creek, North Fork Catoctin Creek, South Fork Catoctin
Creek, Little River, North Fork Goose Creek, Beaver-dam Creek, Piney
Run, Jeffries Branch, Cromwells Run, Hungry Run, Bull Run, Sycoline
Creek, Tuscarora Creek, Horse Pen Run, Broad Run, Sugarland Run, Elk
Lick, Limestone Branch, and as many lesser streams.

The general slope of the county being to the northeast, the waters,
for the most part, naturally follow the same course, as may be readily
perceived by reference to maps of the section. The streams that rise
in the Blue Ridge mostly flow to the eastward until they approach the
Catoctin Mountain, where they are then deflected more toward either
the north or south to pass that range by the Northwest Fork and Goose
Creek, or by the Catoctin Creek which falls into the Potomac above
Point of Rocks. East of Catoctin Mountain the streams pursue a more or
less direct northern course.