266 Tlie Parallel Drift- Hills of Western Neiv York. 



througli which the waters circulated sh)wly toward the gate 

 whence they were discharged from the lake-basin. The gate, 

 we assume, for reasons already stated, to have been the Mohawk 

 Valley. 



During this period the ice was still retreating; and finally 

 the St. Lawrence valley was opened. The waters then sank be- 

 low the summit-level of the MohaAvk, and have since flowed in 

 their present channel. 



This last change must have occurred with comparative ra- 

 pidity, for the waters of Ontario sank so ra2:)idly as to have 

 formed no beach between the old Lake Kidge and its present 

 level. Now, had this change been due, as is believed by many, 

 to an elevation of the land, we might reasonably expect to find 

 some intermediary beaches. That an elevation of land was in 

 progress is not doubted ; but that an elevation, continental in 

 extent, should have occurred with such rapidity as to have pro- 

 duced the effects ascribed to it in the lake region, seems at least 

 problematical ; while the giving way of an ice-dam in the upper 

 St. LaAvrence valley i3resents no such difficulties. 



During the progress of this final recession of the waters of 

 Ontario, the drift in the region of the parallel hills suffered con- 

 siderable erosion, evidences of Avhicli are found in the river 

 valleys, and in the gorges of the small streams leading into the 

 bays along the lake shore. Naturally, the valley of the Oswego 

 Eiver exhibits the best evidences attainable of the erosion of 

 this period. Here a]-e found heavy beds of sand and gravel, far 

 above the present channel, to mark the rush of those ancient 

 waters. 



NOTE. 



In the compilfition of the accompanying map, the writer has to acknowl- 

 edge his indebtedness to the cliarts of tlie U. S. Lalve Survey, the prelimin- 

 ary maps of the New York State Survey, the Geological Survey of New 

 York, the Geological Railway Guide, by James MacFarlane, Ph. D. ; 

 Mr. O. S. Wilson, Assistant in Charge, N. Y. State Survey; and Mr. E. A. 

 Doane, Chief Engineer, R, W., & O. R. R. 



His thanks are also due to Prof. R. P. Whitfield, Curator of the Geo- 

 logical Department of the American Museum of Natural History, for the 

 determination of fossils, and for much other valuable assistance. 



