148 GEORGE C. MATS ON 



approximately its preglacial course. It is possible, then, that 

 these may be interglacial channels, but it would be just as 

 impossible to have them all formed in one interglacial period as 

 to have them all formed during normal stream development. 



The hypothesis that some of the gorges were cut because of 

 drift obstructions requires no different conditions from thoSe 

 existing in scores of places near here. Ten Mile Creek has been 

 forced to cut three short postglacial gorges, because of such 

 obstructions. The acceptation of the above hypothesis calls for 

 a greater number of epochs of deglaciation than has heretofore 

 been recognized in this region; but when we consider the great 

 complexity of drift deposits, which has been recognized else- 

 where, we do not feel that it is necessarily an objection. This 

 hypothesis has no facts opposed to it, while all the others are 

 open to objections which arise from conditions in the field ; 

 therefore we may regard it as established. 



Age of the gorges. — A considerable lowering of the divide 

 between the Cayuga River and the northward-flowing streams 

 might have produced a rejuvenation of the streams tributary to 

 Cayuga Valley. There is, however, little doubt that the Lauren- 

 tian streams were stronger than the Susequehanna; consequently 

 such a rejuvenation at the time of the first glacial invasion is 

 improbable. What may have been the exact conditions govern- 

 ing the erosion at the divide during the remainder of the glacial 

 period is, as yet, unknown. 



Ten Mile Creek was a small tributary near the source of the 

 preglacial Cayuga River, and would not feel the effect of an 

 uplift until long after the rejuvenation had begun in the lower 

 reaches of the stream. It is also questionable whether the uplift 

 occurred long enough before the glacial period to permit the 

 rejuvenation of the entire Laurentian drainage before its lower 

 reaches were obstructed by ice. Nevertheless, the possibility of 

 such rejuvenation must not be ignored. 



paper. Among the best known and most extensive are those of upper Ohio, described 

 by Chamberlain and Leverett, Ainericaii Journal of Science, Third Series, Vol. 

 XLVII, No. 280, pp. 247-82. For descriptions of local reversions see Physical 

 Geography of New York (1902). 



