BOUNDARY OF THE GLACIATED AREA. 149 



tral counties of Pennsylvania are covered with forests, and 

 are cut up into gorges extremely difficult of access. Never- 

 theless, in Lycoming county, upon a plateau at Rose Valley, 

 three or four miles to the east of Lycoming Creek, and sev- 

 eral hundred feet above it, large kettle-holes with their sur- 

 rounding ridges of gravel, and their accompanying bowlders 

 and striated rock-surfaces, are marked features of the land- 

 scape at a height of 2,000 feet above the sea ; while upon 

 the west side of the creek these features are totally absent 

 for some miles above. Similar developments are met, at 

 occasional intervals, all along the line of the great conti- 

 nental divide in Potter county, whence the waters flow to 

 the widely separated regions of the Gulf of St. Lawrence, 

 Chesapeake Bay, and the Gulf of Mexico. The same pro- 

 nounced features already described mark the terminus of the 

 great ice-sheet where it crossed the valley of the various tribu- 

 taries entering the Alleghany River from the north, in Cat- 

 taraugus county, N. Y. In that State these are specially 

 noticeable at Ellicottville, at Little Valley, and upon the 

 high lands upon either side of the Eastern Branch of Cone- 

 wango Creek near Randolph. As the glacial margin 

 swings back again to the Pennsylvania line, it is marked by 

 numerous and impressive accumulations in Warren county, 

 one of the most accessible and notable localities being where 

 it crosses the valley of Conewango Creek at Ackley, a few 

 miles above its junction with the Alleghany River at Warren. 

 Here the marginal line of glacial deposits may be clearly seen 

 as it descends from the highlands on the east diagonally to 

 the valley, filling it to a great depth, and rising over the hills 

 in its onward course to the southwest. At this point in the 

 valley, as at some other places which could be mentioned, 

 the northern side of the moraine is more abrupt than the 

 southern. 



It was here that we made some of our first and most 

 exact discoveries as to the limit of the ice west of the Alle- 

 ghanics. Professor Lewis and myself, who were pursuing 

 the investigations together, had already learned the charac- 



