CAPE COD GEOLOGY 



33 



from the latest Tertiary, although the glacial origin of certain beds in the Pleisto- 

 cene of Marthas Vineyard had been suggested by Shaler in 1888. 1 



McGee 2 first recognized the Pleistocene age of certain deposits that are 

 older than the so-called terminal moraine on the Atlantic slope. After Chamberlin 

 had made his masterful survey of the drift sheets of the Mississippi Valley, McGee 

 established the existence on the Atlantic slope of a group of Pleistocene deposits 

 which he called the Columbia formation. This formation ' 'underlies and is older 

 than the moraine-fringed drift sheet of the northeastern United States." 3 



In summarizing his work on the Columbia formation, McGee 4 interpreted it 

 as representing a first glacial epoch, as passing northward into lower till, and as 

 separated by a long interglacial epoch from the well-known glacial deposits of 

 the northern states, the second glacial epoch of his Conspectus, the Wisconsin 

 glacial drift of current geological nomenclature. 



Shaler, in a revision of his own work on the Gay Head section, published in 

 1890, 5 reaffirmed his belief in the glacial origin of the infolded conglomerate bed 

 in the series but remained undecided between a late Tertiary and a Pleistocene 

 date for the epoch of glaciation. In a section of the Gay Head cliffs prepared by 

 me under Shaler's direction, the glacial gravel, sand, and associated material 

 that lies above the Miocene and unconformably beneath the latest or Wisconsin 

 drift are called interglacial and preglacial, and are grouped in three divisions, as 

 follows, in ascending order : 



8. Sands and clays 



7. Ferruginous sands 



6. Gravel and boulder beds 



In this work it was shown that the glacial series in the Gay Head section, no 

 matter how much infolded and overthrust by Miocene and Cretaceous beds, are 

 comparable with the latest drift of the surface moraine and lie stratigraphically 

 above demonstrable Tertiary beds. A small patch of fossiliferous sand that 

 overlies the Miocene greensand and that was later referred to the Pliocene system 

 was not included in the section as drawn. Shaler's paper showed that, on Marthas 

 Vineyard, deposits essentially like the Pleistocene glacial deposits had been 



1 Shaler, N. S., Geology of Marthas Vineyard, Seventh Ann. Rept. U. S. Geol. Survey, pp 336-337, 

 1888. 



2 McGee, W. J., Three formations of the middle Atlantic slope, Am. Jour. Sci., 35, pp. 120-143, 328- 

 330, 367-388, 448-466, 1888. 



3 McGee, op. cit,, p. 461. 



4 McGee, Conspectus of American Quaternary phenomena, op. cit, p. 462. 



5 Shaler, N. S., Tertiary and Cretaceous deposits of eastern Massachusetts, Bull. Geol. Soc. America, 

 1, 1890, pp. 443-452. 



