66 H. L. FAIRCHILD — ICE EROSION THEORY A FALLACY 



History of the valleys — Preglacial conditions. — It does not seem proper 

 to leave the subject of the Finger Lakes valleys with only a negative 

 conclusion. Following is an outline of the sequence of geologic events, 

 as the writer interprets the history. 



A brief statement has been given on page 56. During the immensely 

 long pre-Pleistocene time the region was probably exposed -to subaerial 

 erosion, and many changes must have occurred in land movement and 

 attitude of the region, which had effects on the development of the 

 drainage. The final result was the north-flowing streams and the hard- 

 rock topography which we now find partially buried under glacial and 

 lacustrine drift. A careful and patient investigation, without too much 

 theorizing far in advance of facts, will probably discover some of the 

 geologic events in the history, specially the later ones. Possibly there 

 may be geologic factors involved of which we have not thought. The 

 great desideratum for the study is data concerning the rock forms. 



Preglacial drainage. — The regularity and parallelism of the north- 

 ward drainage is a striking fact, doubtless explained in part by the 

 uniformity in structure and attitude of the comparatively soft strata. 

 It is believed that at least the stronger streams, such as the Senecan 

 and Cayugan rivers, were graded to the Ontarian river, but with a high 

 gradient. 



The north-flowing streams were so closely spaced that the east-west 

 streams were short and weak. Possibly in this may be found a hint of 

 one cause of discordant drainage. Whatever may be the truth regard- 

 ing this in other regions, in this area any serious discordance must be 

 explained by the interaction of subaerial agents, with this qualification, 

 that the very moderate amount of ice planing on the sides of the larger 

 valleys in some places may possibly have accentuated the abrupt termi- 

 nation of some high-level side valleys, but this widening of the valleys 

 has not been an important effect. 



Ice invasions. — We may not be positive regarding the number of 

 ice invasions in central New York. At present we have evidence of 

 only one, the Wisconsin ; but the certainty of several glacial epochs in 

 the Mississippi region and the accumulating evidence of more than one 

 epoch in the NeAV Jersey-Long Island district, with the evidence of inter- 

 glacial epochs at Scarboro Heights, Ontario, should make us watchful for 

 records of multiple invasions here. 



On first thought it might seem as if the occurrence of ice invasions 

 previous to the Wisconsin would be favorable to the argument for ice 

 erosion, but such is not the case. If the invasions were separated by 

 long interglacial epochs, giving opportunity for mature stream work, the 



