DELTAS IN FEONTAL GLACIAL LAKES. 469 



formed'. I have no proof of any such fiords extending into the ice that 

 did not j^roceed from the broadening' of the channel of a glacial river. Nor 

 is it here assumed that they were at all times filled with salt water. They 

 were perhaps more nearly estuarine, with brackish- water. 



The border clay is here and there strewn with nonpolished bowlders 

 which have typical till shapes. They must either have been transported 

 by floating ice or have dropped from glacier ice. In this case, as well as 

 in that of similar bowlders in the marine clays, I prefer the interpretation 

 of floating ice. I can not perceive any way of regarding these as proof of 

 an advance of glacier ice after the deposition of the clays. They do not 

 constitute a sprinkling of till, much less such a sheet as would be left if 

 the ice readvanced over the clays, or if the border clay were formed sub- 

 glacially. I see no admissible interpretation but that the osar terraces and 

 the border clay were both laid down in channels open to the air. The 

 angular bowlders overlying the border clays are found up to 400 feet. In 

 part they must be due to floating ice of the sea, but there must have been 

 ice floes or little bergs floating in these broad glacial channels, which, as 

 they melted, dropped their burden upon the clay. Some of these bowlders 

 are 8 or 10 feet in diameter. 



The narrow marine deltas, the broad osars, the border clay, the broad 

 solid or plain-like massives, all unite with the lake deltas and the kames, 

 eskers, and osars themselves to prove the gradual enlargement of the chan- 

 nels and pools within the ice. Both subglacial and superficial streams 

 could not only hold their own against the inflow of the ice tending to close 

 the channels but coiild enlarge them. 



DELTAS DEPOSITED BY GLACIAL STREAMS IN FRONTAL GLACIAL 



LAKES. 



The best examples are situated in Dixmont and Unity and are described 

 elsewhere.^ All are small, only 5 or possibly in one case 10 miles long. 

 Regarding the frontal lakes, it is here only necessary to remark: (1) They 

 mark stages in the retreat of the ice northward. (2) They collected between 

 the ice front on the north and hills situated to the south. Thus on a small 

 scale they were equivalent to the lakes that fringed the southern border of 

 the ice-sheet in central New York and Ohio. (3) They differ in no essential 



1 See pp. 141, 146. 



