GLACIAL MARINE DELTAS. 375 



highest level of the sea in the coast region. Marine clays and these 

 so-called, marine deltas are fonnd at all elevations up to about 230 feet near 

 the coast, biTt the deltas have their maximum development as we approach 

 that contour. Above that elevation the deltas are few and rather small, 

 and are situated in the interior valleys. They are found at no 23revailing 

 elevation, and they are local, not confluent like the great deltas found at 

 230 feet or not far above and below. The locality before named in York 

 ai:id Cumberland counties is the best place for the study of the confluent 

 marine deltas. To the careful observer in the southern parts of the State 

 the contrasts between the surface deposits and characteristic scenery above 

 the level of about 230 feet and those below that level is very great. In 

 passing from one of these regions to the other we find a change such as in 

 human affairs would be termed a revolution. The contrast is greater near 

 the mouths of the great glacial rivers than away from them. It should be 

 noted in this connection that the opinion is elsewhere expressed that the sea 

 stood at higher levels 50 or more miles from the present coast than along 

 the outer coast itself 



In the above discussion it is assumed that the broad rounded or fan- 

 shaped deltas were deposited in the open sea. It is a possible hypothesis 

 that they, as well as the narrow marine deltas, were formed subglacially, in 

 places where the subglacial channels had enlarged themselves laterally as 

 they entered the sea, so that broad portions of the ice were undermined and 

 floated on the sea water. This would make the ice approach the condition 

 of glaciers which flow into a warm sea, where they are melted from beneath. 



1. The Waldoboro and other short peripheral moraines prove that the 

 lower portions of the ice contained much morainal matter, though we do not 

 know how great a height it attained. Unless the supposed broad subglacial 

 river should melt all the part of the ice containing morainal matter, there 

 would still remain till in the ice above the channel. As the undermelted ice 

 fell off in icebergs, more or less of this de'bris would fall upon the under- 

 lying gravel and sand. The delta-plains are covered by no sheet of till, 

 though, like the marine clays and all the rest of the country below 230 feet, 

 they are strewn with occasional bowlders, which I attribute to ice floes. 



2. The supposed caves beneath the ice must have been of mammoth size 

 More than a score of the deltas contain a surface of more than 5 square 

 miles each, and several of them contain two or three times that area. 



