GLA.CIAL GRAVELS OF COASTAL REGION. 389 



rates of precipitation, changes in seasonal temperature, and other chmatic 

 conditions — that a glacier can grow thinner and finally disappear without 

 change in the horizontal position of the neve border. But in the case of a 

 great ice-sheet, subject to other than local conditions, it seems to be highly 

 2)robable that there was a retrogression of the neve' border comparable with 

 the retreat of the ice front itself. If so, there must have been a time when 

 the area of the zone of wastage from melting attained a maximum over 

 Maine. Previous to that time part of the zone of wastage had extended 

 southward, where the ocean now is, and took the form of iceberg discharge. 

 As the n^ve border retreated north the area of wastage by melting that was 

 over the land broadened till the time when the outer margin had retreated 

 back to the present coast. Whether the n^ve border of the ice front would 

 retreat the faster after that is uncertain, since we do not know what effect 

 the rising sea had in melting the ice before it. Leaving open the question 

 as to Avhen the area of the zone of wastage from melting over Maine was 

 greatest, we can at least conclude that so rapid a decrease in the quantity 

 of gravels as takes place within 30 miles of the coast could not have been 

 caused, unless in small measure, by changes in the jDOsition of the iiiye 

 line. This may have had some effect, but it seems improbable that its 

 effect could all be concentrated within so narrow a belt and be so con- 

 spicuous here while hardly traceable elsewhere. 



The causes above stated account for the great development of the 

 gravels near the highest level of the sea, but throw only partial light on 

 the causes of the rapid decrease in the gravels toward the coast. The 

 subject is so closely related to the fact that as the gravels become scant v 

 they also become increasingly discontinuous, that the further treatment of 

 the subject is postponed and will be considered in connection with the latter 

 topic. 



SUMMARY. 



The most important characteristics of the glacial sediments of the 

 coast region are the following: 



1. Most of the systems contain one or more marine deltas situated at 

 different distances from the coast. These deltas are interpolated in the midst 

 of the linear series of glacial gravels that Avere deposited within ice walls. 



2. The continuous osars and osar terraces of the interior as they 

 approach the coast break up into ridges separated by intervals. Toward 



