GLACIAL WATERS IN CENTRAL NEW YORK 



41 



C Changes subsequent to the formation of the deposits. 



(A) The transporting ability of a stream is a function of its 

 velocity and volume; but as streams are seldom full loaded the 

 actual work done in the way of supplying delta material depends 

 not only on the. ability of the stream but on the quantity and 

 quality of the detritus supplied to it. Probably none of the glacial 

 streams represented by channels depicted on our maps lacked 

 power to carry all the finer detritus supplied" to them, but in a 

 few localities where the flow was sluggish, as indicated by the 

 low gradient and lack of definition in the channels, we find the 

 stream beds littered with boulders which the currents had been 

 unable to roll any further. Examples may be found in the indef- 

 inite channels between Victor and Phelps. 



The delta-forming materials were derived from several sources: 



(1) Detritus from land drainage, contributed by tributary streams; 



(2) contributions by the glacier drainage or the outwash from the 

 melting ice sheet; (3) glacial drift, the rock rubbish received 

 directly from the ice by those streams which laved the ice front; 

 (4) the glacial drift moraine and kame, which the ice and its 

 drainage had left within reach of the stream; (5) the bed rock 

 encountered by the stream in its down cutting, which in many 

 cases was the most important supply. 



As the streams along the ice border were cutting across ridges f 

 between the great valleys, they did not commonly drain extensive 

 land area and consequently received relatively small contribution 

 from tributary streams. The land-stream drainage was mainly 

 concentrated in the larger valleys, which held glacial lakes, and 

 which were the catchment areas for both the land-stream detritus 

 and that of the proglacial streams. The best examples of ice 

 border rivers with tributary land area are: at Leroy, receiving 

 Oatka creek; at Honeoye Falls, receiving Honeoye creek; at Man- 

 chester., receiving Canandaigua inlet. 



The ice border streams received their detritus mainly from two 

 sources: (a) glacial drift, contributed by the melting ice front and 

 by the streams draining the glacier, and (b) the product of the cor- 

 rasion by the stream on its own channel. Probably the drift borne 

 by the ice sheet had unequal horizontal distribution, and certainly 

 the glacial drainage concentrated the drift at the points of issue 

 or debouchment of the streams. The tendency of the streams 

 draining the glacier to follow the valleys or land depressions beneath 

 the ice sheet resulted in the piling of the stream detritus by the 



