EVIDENCE OF SALMON CREEK. 349 



rise gradually on either side to the plateau level, many hundred feet 

 above the lake. In the valley bottom there is a drift accumulation, with 

 a depth of a hundred or more feet, through which the stream has cut to 

 the rock beneath. 



On the lake shore and in the side gorges the shale can be traced in 

 outcrops with practical continuity to the mouth of this valley on eithe 

 side, so that the preglacial continuation of the valley is not buried beneath 

 drift in the present hillside. There is no gap in the series of outcrops 

 with a width of more than 200 yards. 



Without considering whether the lake valley bottom may not have 

 dropped down, I see but three possible explanations of this phenomenon. 

 Possibly the river bottom may be in one of these narrow gaps. Aside from 

 the improbability of a mature stream being suddenly transformed to a 

 narrow, young gorge at the very point where there happens to be a drift 

 deposit, the evidence in Six-mile creek, and in the buried channels just 

 mentioned, is against this ; and it might also be asked, where are its coun- 



IciTiitQq. Jjjcikc SaXTTvorv Crt£k^ 



toooft 



Figure 1. — Cross-section of Lake Cayuga Valley opposite Salmon Creek. 

 Vertical and horizontal scale the same. 



terparts, for such a condition would necessarily be widespread, not local. 

 A second theory may be that the lakeward continuation of the stream 

 (figure 1 ) was marked by a fall of 350 feet in less than a mile, notwith- 

 standing the fact that the normal fall is but a few feet to the mile. This 

 is so extremely improbalile that it ma}^ be dismissed. The third theory 

 is that the north and south valley has been ice-worn, while the tribu- 

 taries stand at their preglacial elevation, except in so far as they are drift- 

 mied. 



Opposite Salmon creek the lake has a depth of 330 feet. The valley 

 of the creek is a rock-bottomed valley of mature type, distinctly not post- 

 glacial, but of the usual type of this region ; and the rock bottom of this 

 valley is about 20 feet above the present lake surface. We can, I think, 

 assume that this valley, which is transverse to the ice motion., was not 

 sensibly deepened, probably not deepened at all, but always more or less 

 clogged with drift, as it was when the ice disa23peared. Consequently 

 we have here approximately the true level of preglacial Cayuga river. It 

 was 20 feet or thereabouts* above the present level of the lake surface 



*The observation in Salmon creek is not exactl\^ on the lake shore, and the channel of Cayuga 

 river may have been on the western margin of the valley; hence this elevation is liable to an error 

 of a few feet. 



