RECONNOISSANCE OF THE ELIZABETH ISLANDS 401 



From the location of the islands and the general character 

 and arrangement of the material of which they are composed, it 

 is evident that they represent a partially submerged morainal 

 ridge, probably a portion of the later, northern branch of the 

 terminal moraine, represented by Orient Point on Long Island, 

 Plum Island, Gull Islands and Fisher's Island. That these repre- 

 sent a more recent stage of glacial action than Montauk Point, 

 Block Island and Martha's Vineyard is also strongly indicated 

 by the almost total absence of Cretaceous material, which is so 

 characteristic of the earlier or southern branch of the moraine. 

 Nearly all of this material, on account of its incoherent char- 

 acter, would almost inevitably have been eroded on the first ad- 

 vance of the ice sheet over the Buzzard's Bay and Vineyard 

 Sound area, and subsequently incorporated in the first moraine, 

 as we find to be the case on Martha's Vineyard. A precisely 

 similar case is also presented by the eastern end of Long Island, 

 where the older branch of the moraine, represented by Montauk 

 Point, contains practically all of the eroded cretaceous material, 

 while the more recent branch, represented by Orient Point, con- 

 tains almost none.^ 



Under the circumstances we may consider it as peculiarly for- 

 tuitious that the limited exposure of plastic clay on Nonamessett 

 has been preserved, while the close proximity of this to the main- 

 land indicates that there may yet remain some isolated patches 

 which have resisted or escaped erosion, farther up the old estuar- 

 ies, where theoretically the formation once extended. 



Whether the ridge represented by the Elizabeth Islands was 

 caused by an inequality in the crystalHne rocks beneath we are 

 hardly in a position to say, but reasoning from analogy the 

 probabilities are against this idea and the inferential relations be- 

 tween these rocks, the Cretaceous clays and the Drift deposits, 

 according to the facts now in our possession, I have endeavored 

 to indicate in the accompanying section from New Bedford to 

 Martha's Vineyard. [Plate XIV, Fig. 2.] 



1 For more extended discussion of this phase of the subject see : Trans. N. V. 

 Acad. Set., XII (1893), 189-202; 222-237; XIII (1893), 8-22; (1894), 122- 

 132; XV (1895), 3-10; XVI (1896), 9-18 and A>in. A^. V. Acad. Sci., XI 

 (1898), 55-88. 



