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CAPE COD GEOLOGY 



Effects of the Wisconsin Ice Sheet 



The present form of Marthas Vineyard is due primarily to the action of 

 glaciers and glacial streams, and only secondarily to the later work of currents, 

 waves, and winds. Stream erosion since the retreat of the Wisconsin ice sheet 

 in this region has played only a small part in the development of the topography. 

 Stream erosion before the advent of this ice strongly influenced the form and 

 distribution of the Wisconsin deposits. 



Fig. 5. — Map showing position of the lobes of the Wisconsin ioe sheet on Marthas Vineyard at the time of the farthest 

 advance of the ice. 



Marthas Vineyard is a typical interlobate part of the terminal moraine and 

 represents the southern limit of the action of the Wisconsin ice in this region. 

 The ice covered at one time the two northern areas of the island but did not 

 extend to the great outwash plain, except perhaps temporarily to its northern 

 border. The presence of the ice in one part of the island and not in another 

 caused the difference in the topography of these parts. The advancing ice found 

 here no hard rock, but only the Cretaceous and later beds of clay, sand, and 



