CAPE COD GEOLOGY 



169 



is composed largely of reworked glacial and perhaps of some reworked Cretaceous 

 material, laid down at a time of considerable submergence. 



Relation to Older Deposits 



The Gardiners clay probably rests conformably on the gravel near the mid- 

 dle of the Nashaquitsa cliffs section, but unconformably on the deposits at the 

 east end of Nashaquitsa cliffs and at Norton Point. At Gay Head cliffs the 

 Gardiners clay does not form a part of the section, except at the north end, but 

 it is found on the shore east of the cliffs, where it dips away from the cliffs. 

 It therefore seems that the Gardiners clay was deposited around the area now 

 occupied by the cliffs at a time when they probably formed an island. This same 

 relation is seen at Norton Point. Thus the clay lies conformably upon earlier 

 deposits at some places and unconformably at other places. This fact seems to 

 show that when the deposition of the Gardiners clay began the region was only 

 partly submerged, and that the water in which the clay was deposited was 

 not very deep. 



The beds of Gardiners clay have, of course, been considerably distorted by 

 later advances of the ice and the evidence shown by their relations to older 

 deposits is therefore not altogether reliable. At the boulder point on Nashaquitsa 

 cliffs the clay has been thrust against the older beds, and at many places it has 

 been overthrust on itself, or even on later beds. 



Structure 



At many places the Gardiners clay shows a laminated structure, due to its 

 original bedding. The laminae average about half an inch in thickness. With- 

 out these laminae it would be a dense, homogeneous clay throughout, except 

 in some places near the top, where it is interbedded with layers of fine sand. 

 The larger structural features of the Gardiners clay are folds and overthrusts. 

 At some places the clay bed is nearly horizontal; at others it has been closely 

 folded; and between these two extremes there are all gradations. At some places 

 where the clay has been subjected to lateral pressure the beds have been thick- 

 ened and thrown into small folds. Small faults that have slickensided faces have 

 also been seen in the clay, but these are probably due to landslips. At some 

 places where another formation has been pushed over the clay both beds have 

 been dragged. Where a large exposed surface of the clay is alternately wet 

 and dry, parting planes have been formed both on the bedding planes and at 

 right angles to them. 



