956 STUDIES FOR STUDENTS 



received the name of pitted plain. The sags, in many cases at 

 least, appear to be intimately connected with the ice edge, and 

 so to be marginal phenomena. 



Not only may morainic plains and valley trains grade into 

 kame areas at their heads, but they may grade into each other. 

 A wide valley train and a narrow overwash plain may closely 

 simulate each other, and in individual cases it is not easy to say 

 whether the deposits are more properly referred to the one or 

 the other of the two classes.^ This is especially true where an 

 overwash plain is developed in a valley. 



At many points near the edge of the ice during its maximum 

 stage of advance, there probably issued small quantities of water 

 not in the form of well-defined streams, bearing small quantities 

 of detritus. These small quantities of water, with their cor- 

 respondingly small loads, were unable to develop considerable 

 plains of stratified drift, but produced small patches instead. 

 Such patches have received no special designation. 



When the waters issuing from the edge of the ice were slug- 

 gish, whether they were in valleys or not, the materials which 

 they carried and deposited were fine instead of coarse, giving 

 rise to deposits of silt, or clay, instead of sand or gravel. 



In the deposition of stratified drift beyond the edge of the 

 ice, the latter was concerned only in so far as its activity helped 

 to supply the water with the necessary materials. 



C. Deposits at ajid beyond the edge of the ice in standitig zvater. — 

 The waters which issued from the edge of the ice sometimes 

 met a different fate. The ice in its advance often moved up 

 river valleys. When at the time of its maximum extension, it 

 filled the lower part of a valley, leaving the upper part free, 

 drainage through the valley stood good chance of being 

 blocked. Where this happened a marginal valley lake was 

 formed. Whenever the ice spread over a land surface sloping 

 toward it, there was the possibility of the development of a lake 

 basin between the ice on one hand, and the land surface on the 

 other. Marginal lakes and ponds arising in these and other 



'Salisbury, Annual Report of the State Geologist of New Jersey, i89i,p. 97. 



