94 BULLETIN OF THE 



of Cretaceous age. It still seems possible that the fragmeiits containing 

 fossils may be in their nature exotic, as are the fossiliferous materials in 

 the beds at Gay Head. It is to be noted, however, that the greenish 

 gray sand in the section containing the fossils differs considerably in its 

 general aspect from the beds at Gay Head. Moreover, there appears to 

 be an absence of lignites in this portion of the Vineyard series. 



The prevailing northwest dips of this section are in contrast to the 

 attitude of the Gay Head series. I have carefully examined the bedding 

 with reference to the theory that the dislocation is due to glacial thrust. 

 I find it impossible to accept this view, for the following reasons. In the 

 first place, the dips are everywhere tolerably uniform, except within a 

 foot or so of the glaciated surface. In this uppermost part of the section 

 the thrusting and dragging action of the ice is distinctly exhibited in the 

 somewhat sharp flexure of the beds, as well as the considerable contor- 

 tion which they present. It seems to me impossible to believe that a 

 steadfast dip such as is shown by these beds could have been produced 

 by the thrust of a glacial sheet. If the dislocation were due to the direct 

 forward movement of the ice, we should have to explain these dips by the 

 supposition either that the beds originally horizontal were thrown into 

 an arched form, and that we have here the northwest side of the anti- 

 clinal, or that the beds were completely overturned in order to produce 

 the existing dips. There is no trace of such an arch exhibited in the 

 section. Indeed, the presence of such a fold is contra-indicated by the 

 fact that the dips increase to the southward, and the hypothesis of a 

 complete overturn finds no support whatever in the facts. Last of all, 

 we observe that the surface of this district apparently retains its pre- 

 glacial topography. A system of stream valleys is traceable over all the 

 section where the Vineyard series of deposits rise above the sea level. 

 The persistence of a pre-glacial topography, manifest even in the details 

 of the surface, — a topography on which the drift materials are simply 

 imposed, — is overwhelmingly against the supposition that the disloca- 

 tions are in any measure due to the action of the ice-sheet. 



In a memoir on the Geology of Martha's Vineyard, prepared for 

 the Annual Report of the Director of the U. S. Geological Survey for 

 1885-86, I have endeavored to show that the deposits at Gay Head, 

 probably of Miocene or early Pliocene age, were formed in a delta at 

 a time when the level of the shore was perhaps not more than 200 

 feet below its present position. If the evidence from the fossils and 

 the physical condition of these Cretaceous deposits is to be trusted, it 

 indicates that in a much earlier time the shore on this part of the 



