450 R. M. Brown — Clays of the Boston Basin. 



advancing ice. The agent of this work has also been con- 

 sidered a local advance, but again the widespread occurrences 

 of these folds indicate the general event rather than a limited 

 one. 



Where the surface has been planed off, as in fig. 3, the ice 

 was supplied with its clay, which it deposited in the drumlins 

 of the harbor and the harbor vicinity. The beds must have 

 been developed previous to the ice advance. Upham's ex- 

 planation, cited above (dated 1883), cannot be considered as 

 applicable for the Boston district, as he demanded a valley slope 

 by means of which the water was held against the side of the 

 glacier so that the warmer water might undermine the edges 

 of the ice. It is not easy to conceive how clays of any amount 

 could be deposited under the ice by such a supposititious theory. 

 There seems to be evidence strong enough to support the belief 

 that some of the clays of the Boston Basin were deposited before 

 the last general advance of the ice ; are therefore inter-glacial 

 in origin. 



New Bedford, Mass. 



