138 G. F. Eaton — Prehistoric Fauna of Block Island. 



to give this ' kitchen midden ' disclosed many marine shells, 

 mainly species now living in the adjacent waters, the most 

 abundant of which were of oysters, clams, and scallops. 

 Mingled with these were a few r bones of fishes, birds, and 

 small mammals." 



The present writer takes this opportunity to express his per- 

 sonal obligation to Prof. Marsh, who thus called attention to 

 the shell-heaps, and through whose courtesy a thorough 

 exploration was made possible. 



Geology. 



Before commencing a description of the shell-heaps, it may 

 be well to state briefly the geographical position of Block 

 Island, and some of the theories concerning its general geolog- 

 ical relation to the adjacent islands and the mainland. An 

 outline map of this region is shown on Plate III. 



That the same geological formations are found on the long 

 series of islands reaching from New York to Martha's Vine- 

 yard, is the decision of geologists who have made a study of 

 them. That the superficial stratum is of glacial origin is also 

 agreed upon by all. Until recently, however, there has been a 

 wide diversity of opinion as to the age of the basal clays that 

 form the lowest visible beds of the series. Several authors 

 have made passing reference to possible connections of certain 

 of these islands with each other and with the mainland, but 

 their discussions have been chiefly confined to geological 

 periods far removed from the present day, while the geographic 

 conditions during post-glacial time, which are of closer and 

 keener interest to the zoologist, have been disregarded. 



Prof. Marsh writes (this Journal, vol. ii, p. 295, October, 

 1896) : " That Block Island was once connected with Long 

 Island is suggested by a glance at a map of the New England 

 coast, and that the same great moraine extended over both is 

 evident from facts well known. An examination of Block 

 Island itself, however, soon proved to me that these glacial 

 deposits were merely a superficial covering, while the main 

 body of the island was formed of much older beds, the exact 

 age of which offers a most interesting problem." These 

 beds, he states, are composed of variegated fresh-water clays 

 similar to the plastic clays of Long Island and Martha's Vine- 

 yard. The indications are that they were deposited in the 

 quiet waters of a basin which was formerly separated from the 

 Atlantic Ocean by a great barrier that has since been destroyed 

 by erosion and subsidence. 



Prof. Shaler, in his " Report on the Geology of Martha's 

 Vineyard " (Kept. IT. S. G. S., p. 304, 1885-6), while treating 

 of this series of islands, refers to the " considerable gap . . 

 which divides Martha's Vineyard from Block Island." Con- 

 tinuing, he says : " The cause of this break is not perfectly 



