NONCONTINDOUS SEDIMENTATION IN lOB CHANNELS. 399 



hills, some of them wholly or largely composed of till. Here great enlarge- 

 ments of the glacial channels were formed in places favoraljle to the pro- 

 duction of crevasses. Both to the north and south of these local deposits 

 the glacial rivers left no gravels, often for a considerable distance. On the 

 whole, we must admit tliat the local situations of such of the coastal 

 gravels as cap hills are favorable to local enlargements of the channels of 

 the glacial streams, and therefore to sedimentation. The slopes of the hills 

 up which much of this sediment must have been transported would also aid 

 sedimentation. In other cases there are no relief forms of the land that we 

 can connect with the positions of the discontinuous gravel masses. Only 

 in part, then, have we field evidence that gravels were deposited at places 

 favorable to local enlargements of the stream channels. 



What effect had the marginal zone of submarine ice on the distribution 

 of the gravels'? 



As elsewhere noted, one of the mounds of the discontinuous Medomac 

 Valley system of gravels lies beneath the moraine at Winslows Mills. The 

 material of this mound is much waterworn. If any of the deposits of 

 much worn gravel can be connected with the marginal submarine ice, it 

 ought to be this, for it bears a definite relation to the ice front at a certain 

 period. The opinion is justified elsewhere that the gravels were deposited 

 and the glacial stream that left them had ceased to flow before the ice had 

 retreated to the position of the moraine. The bars of subangular gravel 

 that lie in front of the moraine at the road from Waldoboro to North 

 Waldoboro may be frontal gravels, or possibly they were deposited in the 

 marginal zone of submarine ice a few rods in front of the moraine. These 

 gravels are only a very little worn and are unique in character. If there 

 were any gravels deposited in the submarine ice, they would probably be 

 more like these than like the more rounded gravels. The rather steep two- 

 sided ridges that form the terminal moraines in the coast region point rather 

 to overhanging ice than to a projecting wedge of submarine ice as border- 

 ing the margin at the times the moraines were deposited. At other times 

 it may have been different. 



If a subglacial river dropped its coarser sediment as it went up through 

 crevasses in the submarine ice, it ought to have deposited its finer sand and 

 clay near by as a delta or overwash apron. Such deposits would be formed 

 near the ice margin, for we can not admit any great breadth of submarine 



