276 GLACIAL GEAVELS OP MAINE. 



will be formed, and if the rate of recession is uniform, these successive 

 moraines become confluent, as a sheet. 



This I conceive to be the best interpretation of the upper or englacial 

 till. Only where the ice was stagnant does it represent the quantity of 

 debris in the ice at the final melting, and only locally was it stagnant. 

 Where the ice was in motion the thickness of englacial till may several or 

 many times exceed the quantity of englacial matter, comparing equal areas 

 of ice and land. 



There are numerous places where the rock is bare of till or the till is 

 very thin. We liere have proof that there were considerable areas of tlie 

 ice that contained no glacial debris at the time of final melting. The inter- 

 pretation of this fact is a matter of doubt. Many of the places bare of till 

 are on the tops of hills that have deep sheets of subglacial till on their 

 northern slopes. The situation suggests that possibly the ice had been 

 robbed of its englacial material while passing up the northern slopes of the 

 hills. We may here have a glimpse of a general scantiness of englacial 

 matter when the ice had become thin and ready to disappear, or we may 

 assume only local deficiency. 



The terminal moraines are from 10 up to 100 feet high. How many 

 years' accumulation they represent is now unknown. The least possible 

 time we could allow is a single season, and an advance of the ice^O. This 

 would give as the utmost admissible thickness of englacial matter 5 to 50 

 feet. But if the ice was stationary, during the subsequent recession a sheet 

 of the same thickness or thereabout ought to have been formed, and it was 

 not so formed. This proves that the hypothesis of stationaiy ice is inad- 

 missible. Structurallji' the moraines, at least those of Maine, can not be 

 explained unless the ice was in motion. The retreatal moraines of the 

 Muir glacier may possibly be a type of some of the moraines of the Andros- 

 coggin glacier, but not of any others. The proof is irresistible that the 

 moraines represent the debris of an area of ice much broader than their 

 bases. The sheet of englacial till that covers most of the land is a more 

 doubtful subject of interpretation. In a given place it may or may not 

 represent terminal accumulations. 



Without venturing on very definite figures, and allowing for great local 

 inequalities, I assume that the ice in Maine at a given place contained simul- 

 taneously only a few feet of morainal matter, perhaps a maximum of 20 



