CAPE COD GEOLOGY 



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has overriden, but as these consisted predominantly of gravel, the till is also 

 mostly gravel. Where it rests on the Montauk till it partakes to some extent 

 of the nature of that bed. 



The Wisconsin till is at some places at least 10 feet thick, and in certain 

 small areas it may be thicker, but it is almost absent at many places where one 

 would expect it to be thickest. Such places are especially numerous in the 

 western area. The till contains no clay and has a loose gravelly structure, differ- 

 ing strikingly from the Montauk till, which is always tough and compact and 

 shows no tendency to slide where it is exposed in cliffs or banks. Exposures of 

 the Wisconsin till that have been opened for only a short time are usually covered 

 with talus. The till is usually not very coarse, the diameter of most of the 

 pebbles being less than 2 inches and the matrix usually being sandy. It con- 

 tains some boulders, but they form only a small part of it. The greater part of 

 the boulders on the island belong not to the till but to the frontal moraine. 



Source of material. — Most of the material of the Wisconsin till was derived 

 from the Pleistocene beds over which it moved, and as these beds consist mostly 

 of unconsolidated gravel and sand the till is loose and gravelly. Its boulders, 

 except those that were picked up from the Montauk deposits, must have come 

 from a greater distance. All its material, both coarse and fine, before it was 

 transported and deposited in earlier Pleistocene time, must originally have been 

 brought from the mainland on the north. 



Relation of the Wisconsin to earlier deposits. — The Wisconsin till lies un- 

 conformably upon the Manhasset formation and other earlier deposits. The 

 surface formed during the Vineyard interval is thus covered by this thin mantle, 

 irrespective of hills or valleys, except at some places in the higher parts of the 

 western area, where the till is either lacking or is so thin as to be indistinguish- 

 able. The sheet of till shows no disturbances such as are seen in all the earlier 

 deposits, having apparently been laid down very gently. The contact between 

 the till and the beds on which it lies is at few places sharp, or at least it cannot 

 be clearly seen, because the underlying bed and the till are very much alike and 

 the uppermost layers of the lower bed have been somewhat dragged, and so, in 

 a sense, incorporated in the till. Where the till overlies a bed of different nature, 

 such as the Montauk or the Gardiners, the contact may be sharp. 



Distribution. — The Wisconsin till is found only in the western and north- 

 eastern areas and in a zone along the northeast edge of the great plain, where, 

 near the end of its stay, the ice extended temporarily over the outwash. In the 

 northeastern area the till is very sandy, but it is fairly well distributed among 



