100 NEW YORK STATE MUSEUM 



glacial flow, and was probably formed by preglacial streams,^ 

 and in that case the land must have been several hundred 

 feet higher to permit the cutting of such a valley. (3) The 

 Mohawk river flows for a considerable distance over deposits 

 of clay, sand and gravel several hundred feet thick.^ (4) At 

 Syracuse borings have shown that the deposits of drift are over 

 400 feet thick.^ (5) South of Oneida lake and north of the 

 Finger lakes are deep deposits of marl, which must have been 

 formed since the glacial epoch. 



Though soundings have not been made in all parts of the depres- 

 sion, the evidence that we have indicates a deep valley which is 

 apparently tributary to the Mohawk river. For the present, the 

 region west of the Genesee river will be left out of consideration, 

 as the deposits of drift in that part are comparatively shallow, and 

 there is presumptive evidence that the drainage was about the 

 same as at the present time. Between Rochester and Lyons is 

 a section Avhich was not cut very deeply, as it was near the divid- 

 ing ridge between the Genesee basin and the Finger Lake basin. 

 From Lyons to Rome there is a sandy plain, underlain to a greater 

 or less degree by glacial and lacustrine deposits, and the depth 

 of these deposits indicates that at one time a great river must have 

 been here. 



Proof that the cutting of this valley was the work of a stream 

 and not of the glacier is found in a comparison of the effect of the 

 glacier on the other formations exposed to its action. Of these 

 deposits there are three formations that are distinguished by their 

 softness, the Medina shales and sandstones, the Salina shales 

 and the Hamilton shales, and in the Salina is to be found 

 the only narrow valley at right angles to the line of flow of the 

 glacier. The Medina deposits at one time occupied a large portion 



^ Grabau, A. W. Geology and Paleontology of Niagara Falls and Vicinity. 

 N. Y. State Mus. Bui. 45. 9:47-51. 

 ^ Grabau, A. W. Geology and Paleontology of Niagara Falls. 9 :46. 

 Carll, J. F. Pa. Geol. Sur. 1=^:363. 



' Geddes, George. Geol. Sur. of Onondaga. N. Y. State Agric. Soc. 

 Trans. 19 : 277-79. 



An. Rep't of the Superintendent of the Onondaga Salt Springs for 1884. 

 p. 18. 



