68 



CAPE COD GEOLOGY 



a product of glacial deposition, but a surface imposed upon a series of contorted 

 and dislocated beds of diverse age and origin — the older glacial drift and the 

 Cretaceous clay — by the overriding action of glacier ice, and here and there by 

 the thickening of a veneer of later rubbly drift. 



Within small areas the ridges and hollows of this pseudo-morainal contorted 

 drift show a certain parallelism of direction, which is curvilinear in places, as in 

 the so-called submarginal moraine on Nantucket. A sudden change in the direc- 

 tion of the axis of such a group of deposits may occur on opposite sides of a more 

 or less arbitrary line, such as a trench or crease, as if it were due to the arrange- 

 ment of ridges and gigantic puckers beneath part of the ice moving diversely 

 toward the general front. 



Owing to the lobular form of the ice front in areas of the New England 

 Islands, the movement of the ice was not everywhere directly southward but 

 swerved to the southwest and to the southeast on opposite versants of a lobe. 

 For this reason, probably, the overturning on No Mans Land, on the east side 

 of the axis of the Narragansett Bay ice lobe, was to the southeast. The opposite 

 effects are seen on Block Island, where the ice pressed southwestward or west- 

 ward, producing overthrust in those directions, with resultant troughs and ridges. 



TENTATIVE CORRELATION OF THE GLACIAL DEPOSITS 

 AND INTERGLACIAL STAGES 



The correlation of the glacial deposits of New England with those of the 

 Mississippi Valley indicated in the following table is tentative only. In the 

 column headed "Deposit" the nature of certain deposits that, theoretically, 

 should occur in the areas indicated, but that have not been found there, are 

 placed in brackets. 



There is little doubt that the terminal moraines and other later drift deposits 

 in New England may be correlated with the deposits of the Wisconsin stage in 

 the interior, and that the Manhasset deposits are the eastern representative of 

 the Illinoian drift of the Mississippi Valley. The Illinoian drift is a relatively thick 

 and widespread sheet, deposited by a Labradorean glacier long after the Kansan 

 drift had been deeply weathered and extensively eroded. The Illinoian deposits 

 were in turn greatly weathered and much eroded before either the Iowan or the 

 Wisconsin stage of glaciation. The Iowan drift, although it is older than the 

 Wisconsin, is probably considerably younger than the Illinoian. It is a relatively 

 thin drift of less extent, deposited by the Keewatin ice sheet. It is not certainly 



