34 



CAPE COD GEOLOGY 



separated from the latest drift of the terminal moraine by long erosion. These 

 deposits extended downward as a distinct group, separable from the determinable 

 Miocene and the remnant of what was later shown to be Pliocene by the readily 

 recognized characteristics of the Columbia formation of McGee. 



In 1897, in continuation of field work under the supervision of Shaler, I 

 made a study and comparison of the sections at Clay Head on Block Island and 

 at Gay Head on Marthas Vineyard. In a report on this work l I presented evi- 

 dence of an epoch of erosion prior to the deposition of the earliest Pleistocene on 

 these islands. All the beds of granitic gravel and sand in the two sections were 

 referred to the Pleistocene because of their stratigraphic relations to the over- 

 lying glacial moraines and because of their relatively slight decomposition as 

 compared with the quartzose and clayey sediments of the determinable Tertiary 

 and Cretaceous beds in the basal parts of the sections. A further reason for re- 

 garding the beds of boulders and sand as glacial and Pleistocene was found in 

 the northern origin of the glacial drift. After examining a section at Sankaty 

 Head, on Nantucket, I grouped the beds as follows : 



Pleistocene Formations, Classification of 1897 



Wisconsin frontal moraine. Last glacial epoch. 



Vineyard interval of erosion. Last interglacial epoch. 

 Tisbury beds; clay, sand, and scattered boulders. 



Erosion interval and unconformity following the Gay Head diastrophe; now referred 



to ice thrust. 

 Sankaty epoch; granitic gravel and sand in folded beds carrying marine fossils on 

 Nantucket. 

 Lower boulder bed; recognized in Gay Head cliffs. 



In 1901, subsequent to the work on Marthas Vineyard, I published an ac- 

 count 2 of the glacial deposits of the Oyster Bay and Hempstead quadrangles, on 

 Long Island, where, below the Wisconsin moraine, an eroded surface was found 

 representing an interval equivalent to the Vineyard interglacial stage, beneath 

 which surface lay gravel and sand separated by a bed of till. To the whole of these 

 deposits the name Manhasset was given, in the belief that it was a local equiva- 

 lent of the "Tisbury beds" on Marthas Vineyard. The names Tisbury and 

 Manhasset were used as local designations, for it was not considered desirable to 

 extend the use of the names of Pleistocene deposits beyond the states in which 

 they are found. Below the Manhasset on Long Island there was also found a blue 



1 Woodworth, J. B., Unconformities on Marthas Vineyard and Block Island, Bull. Geol. Soc. America, 

 8, pp. 197-212, 1897. 



2 Woodworth, J. B., Pleistocene geology of portions of Nassau County and Borough of Queens, 

 Bull. New York State Mus., 48, pp. 617-668, with colored geological map, Albany, N. Y., 1901. 



