GLACIAL DRIFT. 30/ 



mountain, but would be deflected toward the vacant area at the south- 

 east. It seems probable, therefore, that the hills mentioned were 

 moulded with their unusual trend during the decline and departure of 

 the ice-sheet. Such deflection of the lenticular hills is uncommon, their 

 trend being nearly uniform over large areas, gradually changing from a 

 south-east course in Carroll, Strafford, and Rockingham counties, to a 

 nearly south course in the west part of the state. 



The till of Scotland is described by Mr. James Geikie,* as massed in 

 ridges which seem to be somewhat like our lenticular hills, but more 

 prolonged and less prominent. His opinion that these accumulations of 

 the Scottish till were formed beneath the ice-sheet, seems to be true also 

 of the lenticular hills and slopes of New England. The reasons which 

 lead us to this conclusion are the distance of these deposits from the 

 end or outside limit of the ice-sheet, as it probably existed through the 

 greater part of the glacial period ; their difference from the hills and 

 ridges of the terminal moraines there formed ; the trend of the lenticu- 

 lar accumulations ; their composition principally of lower till ; the occur- 

 rence in this till of level sandy layers ; the similarity of the lenticular 

 hills to slopes which rest against ledgy hills, either upon the side which 

 was sheltered from the ice-current or upon that which was fully exposed 

 to it; and the obscure lamination, which may be commonly observed in 

 sections of the lower till, whether in lenticular masses or in flattened 

 sheets. 



Below a thin covering of upper till, the material of which the inner 

 portion of these hills and slopes is formed is the dark and compact lower 

 till, which has been described on pages 9 and 286. It has been shown 

 that the character of this deposit can be explained only by supposing it 

 to be the ground-moraine accumulated beneath the moving ice-sheet. 

 The small proportion of its iron that has become fully oxidized, and the 



* " In the Lowlands the effect produced by the varying direction and unequal pressure of the ice-sheet is 

 visible in the peculiar outline assumed by the till. Sometimes it forms a confused aggregate of softly swell- 

 ing mounds and hummocks ; in other places it gives rise to a series of long smoothly-rounded banks or ' drums' 

 and 'sowbacks,' which run parallel to the direction taken by the ice. This peculiar configuration of the till, 

 although doubtless modified to some extent by rain and streams, yet was no doubt assumed under tlie ice-sheet." 

 — The Great Ice Age, American edition, p. 88; second edition, revised, p. 76. 



This explanation is quite different from that advanced by Prof. N. S. Shaler, respecting the lenticular hills of 

 eastern Massachusetts, in the Proceedings of the Boston Society 0/ Natural History , vol. xiii, pp. 196-203. 

 He supposed these hills in the vicinity of Boston to be remnants spared by the fluviatile and tidal erosion of a 

 once continuous sheet of drift, which had been contained in a glacier that descended the Charles River valley 

 and was deposited at its melting. 



