CAPE COD GEOLOGY 



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the interlobate axis, where water may have found its way out. It would be diffi- 

 cult, however, to sustain this view by pointing out any effects produced by water 

 discharged along this course when the creases were being sunk into the surface 

 of the Eastham plain. Lake Shaler is not marked by shore lines and must have 

 been rather small and of brief duration at the stage of crease-cutting on the 



Eastham plain. 



North Truro Plain 



Intimately connected with the Eastham plain by reason of its similar 

 elevation and the nature of the creases that dissect its surface is the North 

 Truro plain, which terminated the glacial deposits of Cape Cod at Pilgrim 

 Heights. This plain or terrace was made by the erosion of the beds that form 

 the west edge of the Wellfleet high plain from Highland Light southward. A 

 dissected escarpment separates the two plains along a southward-trending line 

 from Highland Light nearly to Pamet River. This escarpment is not, as Wilson 

 supposed, an ice-contact slope; it is an old erosion cliff that was greatly modified 

 by stream action and glaciation. It is one of the most puzzling features in the 

 topography and glacial history of Cape Cod, and it has no counterpart in the 

 entire region except, perhaps, in the Plymouth region about Manomet Hill. The 

 surface of the North Truro plain is creased, as Grabau and Wilson have noted, 

 by very late Wisconsin streams, which discharged from the ice that lay around 

 the eastern, northern and probably the northwestern border of this plain. 

 When and by what agency was the North Truro plain cut down nearly to its 

 present level, which lies below that of the higher plains on the east and south? 

 At what stage of the ice retreat were the creases on the surface of the plain 

 produced, and in what direction did the water escape to the sea? 



The plain was formed by the erosion of a once higher mass, the beds of 

 which are seen in the cliff at Highland Light. It was formed after the pre- 

 Wisconsin deposits were laid down in the Wellfleet tract, because the valleys 

 which intersect those deposits are traceable across the North Truro plain. These 

 valleys in the region south of Highland Light are well shown by the topographic 

 map. If the North Truro plain was cut back after the "hollows" or valleys of 

 the Pamet River type were formed the "hollows" should have been filled to 

 the level of the plain, even if they were afterward partly re-excavated when 

 surface water ran in the creases on the plain and elsewhere. This plain appears 

 to have been formed just before the Wisconsin stage of glaciation. It was prob- 

 ably once much wider and longer. Coarse gravel near Wood End, on the spit 

 at Provincetown, indicates that this spit stands on a shoal that may represent 



