W. Upham — Recent Fossils near Boston. 209 



270 years since the first settlement in Massachusetts, very sig- 

 nificant restriction and extinction can be shown. For example, 

 Professor Yerrill states that dredging reveals the occurrence 

 of great beds of oyster shells a few feet beneath the harbor 

 mud at Portland, where they are associated with the quahog 

 { Venus merce?iaria), scallop {Pecten irradians), and other 

 southern species ; and that the oysters arid scallops " had appar- 

 ently become extinct in the vicinity of Portland Harbor before 

 the period of the Indian shell-heaps, for neither of these 

 species occurs in the heaps on the adjacent islands, while the 

 quahogs lingered on until that time, but have subsequently 

 died out everywhere in this region, except at Qnahog Bay."* 

 Still later and more surprising is the extinction of the oyster 

 from many localities on the coast of Maine and eastern Massa- 

 chusetts, f Native oyster banks in the Charles and Mystic 

 Rivers two hundred years ago were so productive that an 

 •enumeration of the exports from Boston to the West Indies 

 and Spain in 1687 included "oysters salted in barrels, great 

 quantities of which are taken here." Now there probably 

 remain, according to Ingersoll, only two localities on the New 

 England coast north of Cape Cod, where native oysters sur- 

 vive, these being Great Bay in New Hampshire, back of Ports- 

 mouth, and the Sheepscot River in Maine. They are likewise 

 almost wholly wanting on the Canadian continuation of the 

 coast until Cape Breton Island is reached ; but thence west- 

 ward in the Gulf of St. Lawrence they are plentiful, with 

 numerous other southern species, to the Bay of Chaleurs. The 

 extinction of oysters, and of their southern associates, has been 

 rapidly going on from Nova Scotia to Cape Cod since the 

 earliest settlement of the country, due probably not so much 

 to their exhaustion by being gathered for food, or to any and 

 all other causes, as to a progressive refrigeration of the sea ; 

 and this seems referable, as before indicated, to changes in the 

 volume and warmth of marine currents, which changes ulti- 

 mately may have been caused by the former depression and 

 present uplifting of the region of Bering Strait. 



* This Journal, III, vol. vii, p. 137. 



•f- Ernest Ingersoll, Report on the Oyster- Industry of the United States, Tenth 

 Census, 1881. 



