350 R. S. TARE — LAKE CAYUGA A ROCK BASIN. 



or 350 feet above the present lake bottom at this point, and 455 feet above 

 the deepest point in the lake. 



Evidence of Six-mile Creek. — At the head of the lake, in the city of Ithaca? 

 the valley divides — one part, known as the Inlet valley, continuing south- 

 westwardly and then southerly; the other, called Six-mile creek valley, 

 extending in a southeastern direction. The latter is evidentl}^ a tributary 

 to the former, which was the pregiacial main valley. These two valle3^s 

 are the ones which Simonds* and Footef believe to be due to ice action. 

 They are both distinctly pregiacial in form, and are joined l^y mature 

 tributaries. 



These two creeks, in conjunction with two others, Fall and Cascadilla 

 creeks, which are diverted streams, flowing near their mouths in post- 

 glacial gorges, have constructed the delta-flat upon which Ithaca is built. 

 I am unable to state the depth of this delta, but it appears to be deep, 

 and may have a depth of 200 or 300 feet. At present the Inlet and Six- 

 mile creeks flow through it. 



A practically continuous rock outcrop of shale can be traced from a 

 point a half mile north of this valley to an equal distance on the southern 

 side. The valley is even more distinctly rock-inclosed than that of Sal- 

 mon creek, and the lowest point is fully 50 feet al)ove the lake level, and 

 probably more.J 



These are the only two large stream valleys that have been examined, 

 but either one of them taken alone would be suflicient proof of the point. 

 They have been practically undisturbed by glacial erosion, although 

 clogged with glacial drift, and the present rock bottom is essentiall}^ the 

 pregiacial valley bottom ; it certainly was not lower, although it may 

 have been higher. The north and south valley of lake Cayuga is several 

 hundred feet below it, and its depth has without question been caused 

 by glacial erosion. 



Conditions favoring Formation of Rock Basins. — The author does not feel 

 that there is a necessity of supporting the above conclusions by an expla- 

 nation of the manner in which the ice performed its work of basin erosion, 

 for he believes that the facts upon which these conclusions are based are 

 sufficiently definite to warranftheir acceptance ; but, being a recent con- 

 vert to the rock-basin theory of lake formation, and knowing the difficulty 

 which he had in convincing himself that the facts were as stated, he wishes 

 to point out that the conditions here are unusually favorable for the for- 

 mation of rock basins, as well as for their discovery. If, under favorable 

 conditions, rock basins can be formed by glacial erosion, who shall say 



* Am. Naturalist, vol. xi, 1877, pp. 49-51. 



t Notes upon the Geological History of Cayuga aud Seneca Lakes, 1877. 



Jit is difficult to state exactly the elevation, because the stream is locally diverted by the drift 

 tilling of the old valley; but I have preferred to give the minimum. 



