540 JOHN L. RICH 



valley. If it finds this still occupied by the ice, a marginal deposit, 

 either a gravel plain or a delta, will be formed. Which of the latter 

 is formed will depend on whether or not a marginal lake is held up in 

 the tributary valley. When such a deposit is preserved the two points, 

 one where the stream leaves the ice, and the other where it again 

 reaches it, furnish valuable data as to the position and slope of the 

 glacier tongue at the time the deposits were forming. 



TYPE IV. MORAINIC CHANNELS 



None of the morainic channels studied show features worthy of 

 separate description. A short summary of the most characteristic 

 features of such channels is therefore given instead of detailed descrip- 

 tions of individual channels. 



Morainic channels as seen in the region of the Finger Lakes are 

 characteristically weakly developed. They are often short, irregular, 

 and marked in many cases by scarcely more than a modification of the 

 drift into flat, stream-bottom form. Such a condition is what should 

 be expected. The ice while a moraine is building is subject to more 

 or less backward and forward oscillation. Temporary streams are 

 developed here and there, and under most conditions the great 

 amount of morainic debris supplied to these streams causes them to 

 aggrade rather than to degrade ; to build up the channel bottom rather 

 than to cut it deeper. Hence the prevalence of broad, flat-bottomed 

 channels with ill-defined banks. 



TYPE V. GLACIAL LAKE OUTLETS 



Watkins Lake outlets — The outlet of Lake Watkins, held up by 

 the glacier in Seneca valley, has already been described in part by 

 Fairchild^ and later by Watson.^ Both, however, failed to see and 

 describe the most interesting part of the channel — its beginning and 

 the first one and one-half miles of its course. Both described the 

 channel as beginning at Pine Valley (Fig. 7; Elmira sheet, U. S. G. S.) 

 and continuing southward past Horseheads to the Chemung River at 

 Elmira. Pine Valley was considered the site of the lake outlet as is 

 shown by the following from Watson i^ " This channel has an equally 



1 In connection with his folio work, Tarr iirst discovered the part of this channel 

 above Pine Valley. 



2 Bui. Geol. Soc. Am., Vol. VI, 1894-95, pp. 365-68, 



3 N. Y. State Museum Kept., Vol. LI, 1897, p. 74. 



4 Loc. cit., p. 74. 



