THE

JOURNAL OF SCHOOL GEOGRAPHY

A MONTHLY JOURNAL DEVOTED TO THE INTERESTS OF THE COMMON-SCHOOL TEACHER OF GEOGRAPHY.

TERMS OF SUBSCRIPTION.

One dollar a year in advance. Single copies 15 cents. Subscriptions should be sent to the Journal of School Geography, 41 North Queen Street. Lancaster, Pa.

Mss. intended for publication, books, etc., intended for review, and all correspondence, except concerning subscriptions, should be sent to the responsible editor, Richard E. Dodge, Teachers College, 120th Street West, New York City.

GEOGRAPHY OF WASHINGTON, D. C.

The city of Washington occupies a broad triangular area of terraces at the confluence of the Anacostia and Potomac rivers, near the western margin of the Atlantic coastal plain. The Potomac river flows out of the Appalachian province in the great gaps below Harpers Ferry, traverses the Piedmont plateau in a gradually deepening, relatively narrow trough and emerges in a wide tidal estuary as the coastal plain is entered near Washington. Washington is one of the great series of cities situated along the zone of demarcation between the coastal plain and the Piedmont plateau. Trenton, Philadelphia, Chester, Wilmington, Havre de Grace, Baltimore, Washington, Fredericksburg, Richmond and Petersburg constitute a portion of this series and their locations have been determined by a common cause. They are situated on great rivers of the middle Atlantic slope, which traverse the hard rocks of the Piedmont plateau in narrow gorges of considerable declivity. As these rivers reach the soft overlapping sediments of the coastal plain, under which the hard rocks sink, their valleys rapidly widen, falls cease and the heads of tidal estuaries are soon entered. The wide valleys, usually extensively terraced, afford excellent sites for settlements, the heads of tidal

navigation gives occasion for landings, for warehouses and stores and the main stream or its branches falling over the last hard ledges of the rocks afford convenient water power. So it has come that on every river we have had a city built at this border zone. As the rocky shore against which the coastal plain sands and clays were deposited had a nearly southwest and northeast trend and a uniform attitude which has not greatly altered with subsequent tiltings, these cities lie along a fairly straight line.

Two other factors have been prominent in establishing the present relations. One was a general uplift of the great wedge of coastal plain sediments at a moderately recent geologic date, so that the rivers of the Piedmont plateau cut channels across the coastal plain to considerably beyond the present seacoast line. The other factor was gradual depression which followed and is now in progress, in which sea water has flooded the channels far inland to the steeper slopes on which the crystalline rocks rise to the present line of cities. Thus we have the tide water with navigable channels, which was probably a most important factor in locating the cities.

These features are all impressively exhibited about Washington. The greater part of the city itself occupies a fine series of terraces which begin as soon as the Potomac valley emerges into the soft sands and clays of the coastal plain province and which on the north side of the river have added width, due to coalescence with the terraces of the Anacostia river, a branch which rises in the hills north of the main river.

The tidal estuary with reasonably deep channel extends all along Washington and the western portion of the city is at the head of navigation near where the crystalline rocks rise. Farther west the Potomac river is soon confined in a narrow gorge. The western portion of the city which was built on the rapidly narrowing terraces was formerly Georgetown and here there is extensive water power which in times past was employed in flour and other mills of considerable size.

On entering Washington the visitor will at once be impressed with the great width and smoothness of the terraces. They begin near tide water level and, presenting broad expanses of level surface, rise in low scarps and gentle slopes, usually affording good

drainage, to an altitude of from 80 to 100 feet where they extend far back to the slope rising to the higher lands north of the main portion of the city. The Capitol building is situated on the edge of a west-facing projection of the higher terrace which was given unusual prominence by the erosion of Tiber creek that formerly flowed at its foot.

Looking more widely about the Washington region one will soon recognize the fact that the valley has developed from a succession of plateaus or originally a single plateau which was the very smooth surface of the coastal plain after it had received its final wide-spread mantle of Lafayette gravel in the division of geological time, known as Pliocene (see figure). The remnants of this plateau constitute the highest hill tops about Washington, having an elevation of about 300 feet above tide water with a gentle rise to the westward. Standing on the high land at the Soldiers Home or the ridge beyond Georgetown and looking to the south, the east and the north, one will notice that all these high summits fall into line. Wide depressions are cut below this plateau level, but there is an even sky line in every direction which brings out its former continuity with great distinctness. The slopes east of Anacostia river are surmounted by a portion of this plain which extends as a wide tabular surface far to the eastward to the valley of the Patuxent river.

FIG. 1.-G, old rocks; SS, coastal plain; AA', upper terrace; BB', second terrace; CC', third terrace; D, capitol; M, monument; R, river.

At the close of Pliocene time the region was uplifted about 100 feet and the Potomac river began to cut a wide valley in the soft coastal plain deposits. Its width was about ten miles at Washington, the present location of the city being near its center. At the termination of the uplift this wide trough was floored with a thin mantle of the earlier Pleistocene gravels and loams. Next followed another uplift, at first of about 100 feet, but aggregating 200 feet before it ceased, during which the Potomac river cut another trough within the earlier one, down to the present sea