f Sugarland Run in times of freshets. Occasionally when there is high
water in the river the waters pass up the present channel of the run
to the old channel, and then follow that to the river again. This old
channel enters the river immediately west of the primordial range of
rocks, that impinge so closely upon the river from here to Georgetown,
forming as they do that series of falls known as Seneca Falls, the
Great, and the Little Falls, making altogether a fall of 188 feet in
less than 20 miles."--_Memoir of Loudoun_.]

[Footnote 4: Designated in an old record as a "double-bodied poplar
tree standing in or near the middle of the thoroughfare of Ashby's Gap
on the top of the Blue Ridge." It succumbed to the ravages of time and
fire while this work was in course of preparation.]

This completes an outline of 109 miles, viz: 19 miles in company with
Fairfax, 10 with Prince William, 17 with Fauquier, 26 with Clarke and
Jefferson, and 37 miles along the Potomac.

TOPOGRAPHY.

Loudoun County is preeminently a diversified region; its surface
bearing many marked peculiarities, many grand distinctive features.
The broken ranges of hills and mountains, abounding in Piedmont
Virginia, here present themselves in softly rounded outline, gradually
sinking down into the plains, giving great diversity and
picturesqueness to the landscape. They are remarkable for their
parallelism, regularity, rectilineal direction and evenness of
outline, and constitute what is by far the most conspicuous feature in
the topography of Loudoun. Neither snow-capped nor barren, they are
clothed with vegetation from base to summit and afford fine range and
pasturage for sheep and cattle.

The main valleys are longitudinal and those running transversely few
and comparatively unimportant.

The far-famed Loudoun valley, reposing peacefully between the Blue
Ridge and Catoctin mountains, presents all the many varied topographic
aspects peculiar to a territory abounding in foothills.

The Blue Ridge, the southeasternmost range of the Alleghanies or
Appalachian System presents here that uniformity and general
appearance which characterizes it throughout the State, having gaps
or depressions every eight or ten miles, through which the public
roads pass. The most important of these are the Potomac Gap at 500
feet and Snickers and Ashby's Gap, both at 1,100 feet. The altitude of
this range in Loudoun varies from 1,000 to 1,600 feet above
tide-water, an