458 C. R. DRYER — FINGER LAKE REGION OF WESTERN NEW YORK 



During this period lacustrine sediments of unknown depth were depos- 

 ited on the valley bottoms. To this filling is probably due the general 

 flatness of the valley floors above and below the lakes and the absence 

 of surface boulders at low levels. 



Discussion and Interpretation - 



It is time now to attempt an interpretation of the peculiar features 

 their history. On some points of the problem the solution seems clear 

 and hardly open to question. Other points are difficult and obscure. 



1. The absence of all indications of folding or faulting makes it cer- 

 tain that the valleys and ridges are due to erosion. The evidence is 

 equally conclusive that they have been glaciated. The main problem* 

 then, is to determine the part which water and ice have respectively 

 played in their formation. 



2. The hypothesis that this part of the Allegheny plateau was dis- 

 sected in pre-Glacial times by northward flowing streams to a degree 

 approaching maturity is the most obvious one. Their headwaters had 

 eaten back beyond the crest of the plateau and interlocked with the 

 headwaters of southward flowing streams. The Canandaigua stream 

 would seem to have headed south of the terminal moraine at some 

 point down the present Cohocton valley. A similar southward exten- 

 sion may be attributed to the Hemlock stream, and perhaps to the 

 Canaseraga also. 



On its face this hypothesis is met by one serious difficulty. The 

 Cohocton- Wayland valley extends east and west a few miles south of 

 the plateau crest, cutting across and connecting the heads of three prin- 

 cipal northward sloping valleys, and is as wide as any one of them, but 

 with a floor 500 to 600 feet higher. How much of this difference of 

 level is due to glacial filling is unknown, but in the present hypothesis 

 this valley seems incongruous and out of place. It may have been 

 begun by tributaries of the Canaseraga, Hemlock, Canandaigua, or Co- 

 hocton streams — some or all of them ; but that headwater tributaries 

 near the crest of a plateau cut a valley a mile wide] and 1,200. or 600 

 feet deep is a scarcely tenable proposition. 



3. The scheme of Laurentian drainage in Tertiary times proposed by 

 Grabau * postulates the Genesee river as a southward flowing consequent 

 stream, and the Allegheny*- plateau as a cuesta through which it cut a 

 gorge. On this hypothesis, the possibility that the Canaseraga-Cohocton 

 valley is the modern representative of the Tertiary gorge of the Genesee 

 is worthy of consideration. In that case the Conesus, Hemlock, and 



* Bull. New York State Museum, no. 45, pp. 37-47. 



