EELATION OF LOWER TILL TO MARINE GRAVELS. 283 



the Waldoboro moi'aine. At the time the sea stood at its highest level the 

 water would be about 150 feet deep over the top of the island. Here then 

 is a good place to observe the effect of the sea waves on the ice and its 

 contained till as the ice front retreated northward. If this lenticular mass 

 of till was contained in an embayed mass of ice rendered viscous by the 

 amount of solid matter distributed through it, or if it was cast out at the 

 ice front as any kind of frontal moraine, then we ought to find the till more 

 or less assorted by water unless the ice had melted with extraordinary 

 quietness before the elevation of the sea. A inultitude of facts furnished 

 both by the terminal moraines and by the deltas deposited by glacial rivers 

 in the sea, as well as by the valley drift of the river valleys, point to the 

 conclusion that the sea stood at high level during all the later part of 

 glacial time. On Munjoy Hill, Portland, are a number of small irregular 

 masses of sand, filling pockets in the clayey till. They are found only near 

 the surface. In the lower part of the deep masses of till I have found no 

 water-classified matter. The presence of signs of water, either glacial 

 streams or mai'ine waves, in the upper portion of the till only makes their 

 absence in the lower till still more suggestive. 



The relations of the beach gravels to the deep masses of till are not 

 only perfectly consistent with the subglacial origin of the lower till, but 

 distinctly favor this hypothesis. 



On the whole, we may affirm that whether we regard the composition 

 of the lowest portion of till, or its relations to the terminal moraines or to 

 the glacial gravels on the marine deposits,. all find their simplest explanation 

 in the hypothesis of a ground moraine. 



It is not asserted that a ground moraine covered all of Maine. It is 

 well known that many places are bare of till where there has been no 

 erosion by the sea or streams. There are places where probably only sub- 

 glacial till is present, and others where the till was all englacial, or nearly 

 so. Neither is the line of demarcation between these two deposits always 

 sharply defined. Indeed, they graduate one into the other so as often to 

 render it difficult to make out the line of separation. Probably the lower 

 the point in the ice where morainal fragments occui'red, the more glaciated 

 they would be — a sufficient cause of gradations in glaciation between the 

 upper and the lower till. 



