Probably this mountain does not exceed an average of more than 300 feet above the surrounding country, though at some stages it may attain an altitude of 700 feet. Rising near the Potomac into one of its highest peaks, in the same range it becomes alternately depressed and elevated, until reaching the point of its divergence in the neighborhood of Waterford. There it assumes the appearance of an elevated and hilly region, deeply indented by the myriad streams that rise in its bosom. On reaching the Leesburg and Snicker's Gap Turnpike road, a distance of twelve miles, it expands to three miles in width and continues much the same until broken by Goose Creek and its tributary, the North Fork, when it gradually loses itself in the hills of Goose Creek and Little River, before reaching the Ashby's Gap Turnpike. The Catoctin range throughout Loudoun pursues a course parallel to the Blue Ridge, the two forming an intermediate valley or baselevel plain, ranging in width from 8 to 12 miles, and in altitude from 350 to 730 feet above sea level. Allusion to the physiography of this valley--so called only by reason of its relation to the mountains on either side--has been made elsewhere in this department. Immediately south of Aldie, on Little River, near the point of interruption of Catoctin Mountain, another range commences and extends into Fauquier County. It is known as "Bull Run Mountain," but might rightly be considered an indirect continuation of the elevation of the Catoctin, its course and some of its features corresponding very nearly with that mountain save only that it is higher than any of the ranges of the latter, excepting the western. East of the Catoctin the tumultuous continuity of mountains subsides into gentle undulations, an almost unbroken succession of sloping elevations and depressions presenting an as yet unimpaired variety and charm of landscape. However, on the extreme eastern edge of this section, level stretches of considerable extent are a conspicuous feature of the topography. Three or four detached hills, rising to an elevation of 150 or 200 feet above the adjacent country, are the only ones of consequence met with in this section. COMPARATIVE ALTITUDES. The hilly character of Loudoun is clearly shown by the following exhibit of the elevation of points and places above tide-water. The variations of altitude noted in this schedule are based upon conflicting estimates and distinct measurements made at two or more points within a given circumference and slightly removed one from the other.