WAS THEEE AN INTERGLACIAL PERIOD IN MAINE? 289 



•clers may mark an advance of thin ice, but only a temporary one. If there 

 shall be found in Maine unmistakable subglacial till in situ overlying the 

 marine clays, it will indicate a much longer period of advance than any 

 interpretation now allowable. 



8. If the sea rose while the ice still remained, so that the waves beat 

 -upon a shore of ice, pieces of ice would from time to time be detached, 

 partly as floating bergs, but in case of ice containing englacial matter' it 

 might often happen that the pieces would not float because of the morainal 

 matter contained, and when the ice melted such fragments would form a 

 deposit similar to true glacial-transported till. Such might often be lodged 

 in the marine beds or glacial gravels. I have not sufficient facts to discuss 

 the hypothesis at present, yet this question must be considered before the 

 significance of small till masses on or in marine sediments can be regarded 

 as definitely determined. 



The floating bergs would naturally di'op fragments upon the sea bot- 

 tom, and perhaps sometimes quite deep masses. These deposits must be 

 distinguished from matter brought to the place of deposition by glacier ice. 



9. It is agreed that the fossiliferous sands and clays of Portland overlie 

 a fine blue clayey till, apparently subglacial. But on the upper slopes of 

 the hills I found fossiliferous sand overlying glacial gravel. This I regard 

 as beach sand and gravel, composed of the material washe<i down from the 

 top of the hill by the waves of the sea. Glacial sand and gi-avel were 

 originally deposited on the tops of the hills. Part of this deposit and per- 

 haps some till were subsequently eroded by the sea and strewn on the hill- 

 sides. The alternative hypothesis would be that the fossils grew in the 

 sediments of the glacial streams as they were poured out from ice channels 

 into the sea. 



10. In determining whether in a given region there have been two ice 

 periods, we have to compare the shapes of the stones of the till of the 

 supposed two ages. As elsewhere noted, a system of glacial streams is 

 inseparable from a glacier, and these waters leave a system of glacial sedi- 

 ments. If ice subsequently advanced, the rounded stones of this glacial 

 gravel would either be overridden by the later glacier or be partly or 

 wholly eroded and pyished forward by it, and in either case they would be 

 found in either the earlier or later till, perhaps at the terminal moraines. 

 They might be somewhat planed or modified in shape in the process, yet 



MON XXXIV 19 



