CAPE COD GEOLOGY 



35 



clay, the base of which was not seen. This clay was, with some doubt, regarded 

 as a basal part of the older Pleistocene, for which McGee's name Columbia was 

 retained. 



Fuller's determination of the Pleistocene stratigraphy had fixed the position 

 of the beds of laminated blue clay not only on Long Island but on Marthas 

 Vineyard, where their relations to the Pleistocene series had not been clearly 

 made out. It is true that in certain sections on the north shore of Marthas Vine- 

 yard I had included them in the "Tisbury beds," but in our work on the south 

 side of the island neither I nor Shaler had satisfactorily separated these Pleisto- 

 cene beds of blue clay from the Tertiary and Cretaceous beds with which they 

 had been confounded. 



Fuller's determination of the position of the beds of Gardiners clay has made 

 it possible to fix the position of other Pleistocene beds immediately above and 

 below them in the islands east of Long Island, and my associate, Dr. Edward 

 Wigglesworth, has found this clay bed a satisfactory horizon marker for the 

 older Pleistocene deposits on Marthas Vineyard. 



Of the Mannetto gravel of Fuller and the unconformity succeeding it below 

 the Maneco gravel, it may be said that different deposits are found on Marthas 

 Vineyard in an apparently equivalent position, as explained beyond, and beneath 

 them occur deposits that appear to be older than Fuller's Mannetto gravel. To 

 these underlying deposits new names are here given. 



CLASSIFICATION OF THE PLEISTOCENE DEPOSITS 

 ADOPTED IN THIS REPORT 



All the Quaternary deposits on the New England Islands from Long Island 

 eastward to Marthas Vineyard and from the Jameco formation upward to the 

 Wisconsin moraines are easily recognized and singularly persistent, but their 

 equivalents on Nantucket and Cape Cod have not been certainly determined. 

 Below the Jameco gravel, and certainly below the unconformity in the sections 

 at Gay Head cliffs on Marthas Vineyard and at Clay Head on Block Island, 

 there is a complex series of glacial deposits, mainly stratified gravel and sand, 

 which appears to occupy, at least in part, the position in the section assigned 

 to the Mannetto gravel on Long Island by Fuller; but these deposits cannot be 

 correlated with any lithologic equivalent in Fuller's Mannetto deposits. The 

 deposits agree in containing pebbles of feldspar-bearing rocks, such as granite de- 

 rived from the mainland. The chert pebbles found in the Mannetto on Long 

 Island appear to be equivalent to the chert pebbles found in the Aquinnah or 



