SUMMARY. 3-55 



at least, and presumably the others also, had a north flow unless I have 

 entirely misinterpreted the value of the evidence. The mature valleys 

 of the upland tributaries to this main stream had a moderate slope, if 

 we may judge them by their present condition, as seems to me justi- 

 fiable. The evidence of the mouths of the preglacial tributaries brought 

 forward in figure 2 suggests also a moderate slope. The indications are, 

 therefore, that this was the case also beyond the outlet of the present 

 lake in the old valley now buried beneath the drift. Even granting that 

 this river had a very irregular course, it must, provided a deep valley 

 passed through the site of the present lake Ontario, have had an ex- 

 tremely rapid slope, much more rapid than would be expected in a 

 mature stream ; and the diagram (figure 1) might then be used for lake 

 Ontario, substituting the name Cayuga river for Salmon creek, and lake 

 Ontario for lake Cayuga, and at the same time changing the scale. 

 It therefore seems unlikely that it did have this slope, but that the slope 

 which appears to be necessary has been caused by glacial erosion. 



It is interesting to note in this place that, just as in the case of lakes 

 Cayuga and . Seneca, lake Ontario has its greatest depth on its southern 

 side, and that the deepest point of the lake is just north of Cayuga and 

 Seneca, where the greatest glacial erosion in the Finger lake region is 

 accomplished. 



If the above conclusion be true, then we have no proof that the inte- 

 rior of the continent in this region has been depressed since the glacial 

 period, nor that it was higher in preglacial times. 



Summary. 



Briefly summarized, this paper, after a description of the topography 

 of the region and a summary of the opinions previously held, attempts 

 to prove that lake Cayuga, and presumably other of the Finger lakes, is 

 situated in a rock basin with a maximum depth of approximately 435 

 feet. The nature of the proof is that the preglacial tributaries to this 

 valley are found to be rock-enclosed, and that their lowest points are 

 above the present lake surface. 



It presents also a brief discussion of the reasons why a rock basin was 

 constructed with comparative ease in this region ; and a rhythm of glacial 

 erosion and deposition is suggested. The course of the preglacial Cayuga 

 river is found to be northward, probably tributary to a river w^hich 

 drained at least one of the Great lakes, Ontario. As the tributaries of 

 Cayuga river prove the rock-basin origin of lake Cayuga, so also the 

 Cayuga river tributary to the Ontario stream indicates, that lake Ontario 

 is also a rock basin. 



XLIX— Bull. Geol. Soc. Am., Vol. 5, 1893, 



