6o NEW YORK STATE MUSEUM 



alluvial-fan shape across the Tioughnioga valley. Because such 

 filling, then, makes the valley bottom highest on its west side the 

 course of the stream is pushed sharply over against the east side of 

 the valley and made to outline the form of the fans on the north 

 and south. The deposit at Preble is clearly shown in plate i8 where 

 it is seen rising with relatively steep slope up the valley opening in 

 the center of the picture. 



In other words, after the outwash from the Tully lobe had been 

 built up to its maximum level, heavy outwash deposits were still being 

 brought out of the Otisco and Skaneateles valleys and dumped on 

 top of the Tully outwash plain where these valleys had outlet to this 

 plain at their south ends. 



It may be argued that these deposits are of postglacial date, and 

 hence that the pushing of the Tioughnioga stream against the east 

 side of the valley may also have been a recent occurrence and not 

 contemporary with ice-waning phases of the glacial occupation. 

 Such a deduction is, however, opposed by several lines of evidence. 



If of postglacial origin the deposits at the mouths of the valleys 

 would nevertheless need to have been stream-transported. Yet there 

 is no drainage down the southeast slope of the Otisco valley ending 

 at Preble at all competent to build up such a mass. The small 

 stream that does emerge from the valley is apparently itself guided iii 

 its course by the outwash accumulations, for it skirts their south 

 edge and empties into Little York lake. While this applies with 

 less force to the conditions at Homer, for Factory creek is evidently 

 a stream of sufficient length and volume to transport considerable 

 sediment, sufficient proof that it did not make this deposit is found in 

 the fact that Factory creek is an eroding, and not a depositing, 

 stream in this section and has cut a notable channel through the out- 

 wash itself ; is, indeed, engaged in clearing it away. 



Finally, the nature of the channel of the Tioughnioga stream itself 

 gives evidence that it was developed under different conditions from 

 those that now prevail. On comparison of plate 19, which shows 

 the Tioughnioga river in the section where it is forced to flow close 

 to the east valley wall (on the right), with plate 13 of the abandoned 

 lake outflow channel across the Tully moraine, it will be perceived 

 that these have essentially similar characteristics. The Tioughnioga 

 river in this section has the channel peculiarities of a lake outlet 

 stream, and such indeed it is. But the existing stream is " under- 

 fit " (to use a word coined by Prof. W. M. Davis of Harvard) m 

 that it flows over the bed of the channel in wide shallows and 

 has not, under the existing conditions, either the volume or the 



