MORAINES OF VALLEY LAKES 223 



mainly from the material which the small lateral tongue could supply. 

 There are doubtless instances in some localities where the supply fur- 

 nished by the land streams has modified the unequal development of 

 moraines. 



Moraines distinctly traceable for a distance often lose distinctness, 

 and even become untraceable where crossing hill slopes or hilltops at 

 points where there were divides between two ice tongues. Where they 

 do not entirely disappear they sometimes change in character, from 

 kamey areas of stratified drift to low ridges and hillocks of sag and 

 swell type composed mainly of till. These variations are doubtless due 

 to unequal effects of marginal drainage and ice supply similar to those 

 above described. On such ice-divide areas the influence of marginal 

 drainage is reduced to a minimum, and the dominant, and often the 

 sole cause for morainic accumulation is the melting out of rock fragments 

 from the ice front. 



Morainic Complex between Cayuga and Seneca Valleys 



In the hilly country between Cayuga and Seneca lakes there is a 

 morainic complex which seems to have little system. In some portions 

 the moraine bands are traced continuously for several miles ; but where 

 crossing a valley or passing across the hills these are often lost, so that 

 it becomes almost or quite impossible to correlate moraines on two sides 

 of a valley. 



The complexity of the conditions during the ice withdrawal from 

 this region may be understood from the following statement : As the ice 

 melted away the higher hilltops first appeared, and around some of 

 them nunatak moraines were accumulated during a halt in the ice re- 

 cession. These nunatak deposits are rarely continuous and are often 

 not easy to distinguish from parts of moraine belts. A later stage found 

 ice moving complete!}' through valleys, while the inclosing hills rose 

 above its level. In some of the valleys high-level moraine terraces 

 and other moraine deposits furnish evidence of such a stage. The 

 next step in the ice withdrawal may be considered to be that in which 

 free movement through the valleys ceased while stagnant blocks re- 

 mained. Thickened hillside deposits, often of a morainic character, 

 present in many of the valleys and apparently not associated with 

 active ice tongues, are interpreted as deposits marginal to such stagnant 

 blocks. 



After the. stage of stagnant blocks active ice tongues extended into 

 the valleys, sometimes from both ends. During these stages there were 

 built frayed moraines on one valley wall, and often terminal moraines 



XXX— Bull. Geol. Soc. Am., Vol. 16, 1904 



