78 JOHN LYON RICH AND EDWIN A. FILMER 



narrow, postglacial gorges A third condition is where a stream enters 



the earlier gorge, clears out part or all of its drift filling, and follows it across 

 the steepened slope to the main valley. This is certainly the case in lower 

 Six Mile Creek. 



It should be noted that in this reference to Six Mile Creek Tarr 

 makes no distinction between the gorge characterized by the ''broad 

 amphitheaters" mentioned above (our 600-foot gorge) and the 

 gorge of "lower Six Mile Creek," which the stream follows to Cayuga 

 valley (our second, or 200-foot, gorge). 



A following paragraph (p. 281) is especially significant in con- 

 nection with the facts brought out by our recent study. We quote 

 in full: 



This evidence establishes a third point regarding the drainage history of 

 Seneca and Cayuga valleys, namely, that there is an almost, if not absolutely, 

 uniform condition of gorges in the bottoms of the mature hanging tributary 

 valleys; that these gorges, being drift-filled, antedate the last ice advance; 

 that they are broader and deeper, hence required longer time to form than the 

 postglacial gorges; and that, where they enter the main valleys, their rock 

 bottoms are above lake level. They therefore resemble hanging valleys, since 

 their bottoms are in some cases, as Taughannock, about 400 feet above the 

 main valley bottom one-half mile distant. Since we have no data proving what 

 their bottom slope actually is, though it seems evident that their slope is very 

 steep, and possibly great enough to carry them down to the main valley axis, 

 it may not be proper to consider them hanging valleys. If the interpretation 

 of hanging valleys is warranted, which I doubt, then the tributary valleys to 

 Seneca and Cayuga Lakes are double hanging valleys — an upper mature hang- 

 ing valley and a lower hanging gorge valley. 



In the case of Six Mile Creek at least we now have the data 

 proving the actual bottom slope (Fig. 6) and it appears that the 

 slope is, in reality, comparatively gentle, and that the double hang- 

 ing valleys of which Tarr speaks are, in fact, present. 



In another paragraph in the same paper (p. 284) the results of 

 our recent study are foreshadowed in the following words: 



A modification of the glacial erosion theory has been advanced during the 

 progress of the investigation of the problem and is still being considered. It 

 is as follows: During its first advance the ice deeply eroded the valleys; during 

 interglacial conditions the older valleys were cut; with return of glaciation the 

 valleys were deepened still further. During as many glaciations as this region 

 experienced this process was continued. On this basis the older gorges are 

 interglacial; their cause is the lowering of their base level by the overdeepening 

 of the valleys to which they were tributary. Since facts sufficient to establish 



