Page:Origin of the High Terrace Deposits of the Monongahela River.pdf/10

Rh is new. The resultant modifications which such a change of direction in a great river system must necessarily bring to pre-existing drainage lines, are so varied and amazing even in contemplation, that their study must furnish many problems of surpassing interest to topographers of the modern school, so ably typified by Prof. Davis and his work.

he [sic] following table represents the descent of the ancient Monongahela river toward the lake region for a portion of its course between. Weston, W. Va., and Sharon, Pa., as well as the present water levels between the same points, and also the highest levels of the Morgantown beds, where known:

This table shows that while the present river falls 290 feet between Weston and Pittsburg, the floor of the ancient stream descended only 110 betwen the same points, or only about one-half foot per mile, which is practically that of a base-leveled valley, or one quite advanced in age, to say the least. The rapid descent of the modern river below the old rock floor of the ancient one gives rise to the steep slopes and gorge-like character of the Monongahela valley every where between Weston and Pittsburg, while the same is true of the lower courses of all the larger tributary streams, the descent in these being very rapid in the last few miles of their courses, while in their upper reaches the slope is gentle and the topography much older looking.

The smaller streams, which rise only five to ten miles back from the Monongahela, descend to it in the last mile or two of their courses by a series of rapids and cascades, while the still smaller brooks and rivulets have cut more notches in the bounding valley walls below the level of the ancient rock floor