W. U. Davis—Gorges and Waterfalls. 129 
cutting a narrow, gorge-like channel, with bare outcropping 
rocks free from drift for one hundred and twenty-five feet above 
the lake level. Crooked Lake, also in Wyoming county but on 
the other side of the deep valley of the Susquehanna, has the 
same origin; the old valley below the lake is now without a 
stream, for the overflow has turned to one side, first running 
with gentle slope over drift deposits; then descending one 
hundred and ten feet in a narrow gorge over a series of rocky 
cascades. Here it joins Buttermilk Creek, the lower course of 
which has been entirely changed by glacial deposits. Vast 
heaps of drift are piled up in the old channel about the mouth 
of the aneient stream, so that its modern representative is turned 
aside to plunge over the cliffs of Catskill rocks into the valley 
of the Susquehanna. In the deep, narrow gorge that has thus 
been formed, the stream falls eighty feet in several cascades in _ 
a horizontal distance of two hundred yards. The old valley 
can be traced nearly clogged with drift heaps; and the evidence 
of the change in the stream’s course is said to be singularly 
clear and conclusive. 
_ Other post-glacial valleys, with steep rocky walls and very | 
little drift are described by Mr. Carll in western Pennsylvania, 
while the old valleys are broad and deeply filled with heavy 
drift deposits.* 
The most appreciative description that I have found of the 
relation between drift obstructions and river gorges is in Mr. J. 
Geikie’s ‘Great Ice Age.’ Nothing can be more striking—this 
author writes—than the sudden and complete change of scenery 
that ensues upon the passage of a stream from its new into its 
old channel. In the former the water frets and fumes between - 
lofty walls of rock, which, seen from below, appear to rise 
almost vertically from the river's bed. In such a deep, narrow 
gorge the stream may continue to flow for miles, when of a 
sudden the precipitous cliffs abruptly terminate, and the water 
then escapes into a broad vale, with long sloping banks of 
Stony clay, sand and gravel. The burial of old valleys is 
especially common in districts where they stretch across the 
advance of the ice; the gorges of the Avon and the Calder, 
branches of the Clyde, are thus explained as post-glacial cuts, to 
one side of the drift-filled, pre-glacial channels. 
_ Mr. A. Geikie writes of one of the most remarkable go 
in Scotland,t that of the Mouse water, in the district of the 
Cartland crags, near Lanark. The stream descending from the 
shady ravines of Cleghorn flows smoothly for half a mile 
through an old valley still choked up with bowlder-clay. This 
* Geol. Penn., ITI, Oil Regions, 1880, 347. 
+ Great Ice Age, 1877, 133, - 
+ On the Glacial Drift of Scotland, Trans. Geol. Soc. Glasgow, i, pt. 2, 1863, 51. 
» AM. Jour. Sct.—Tarep ry VoL, XXVIII, No, 164.—Auausr, 1884 
