W. TJjpham — Recent Fossils near Boston. 205 



suggests that the Strait of Belle Isle, which is about ten miles 

 wide and 180 feet deep in its narrowest and shallowest part, 

 may have been closed by the elevation, shutting out the cold 

 waters that pour through it, carrying small icebergs and floes 

 into the Gulf of St. Lawrence ; while as great an uplift of the 

 extensive shallow Fishing Banks would ward off the arctic cur- 

 rent far into the ocean. If we had to consider this coast alone, 

 the explanation would seem very acceptable ; but evidences of 

 such warmer postglacial temperature, both of sea and land, 

 succeeded now by a moderate degree of refrigeration, are found 

 to extend over all the North Atlantic region, including also 

 Greenland, Iceland, northwestern Europe, and even Spitz- 

 bergen." We therefore must conclude that these climatic 

 changes probably have depended in common on farther reach- 

 ing causes and conditions, which may yet have consisted chiefly 

 in geographic movements of elevation and subsidence, with 

 their effect on the general oceanic circulation. 



Between the time of departure of the ice-sheet, at the close 

 of the Glacial period, and the time of northward migration of 

 the southern marine fauna, a very important upward movement 

 had taken place, affecting the eastern provinces of Canada and 

 the northern two-thirds of New England, extending south to 

 the latitude of Boston. To speak more strictly, however, this 

 uplifting of our part of the continent was limited southeast- 

 ward by a line drawn approximately from the mouth of the 

 Hudson northeast to Boston and onward through Nova Scotia. 

 When the ice-sheet was being withdrawn from this region, the 

 country south of this line stood somewhat higher than now, as 

 is shown by the channels of streams that flowed away from the 

 melting ice and ran across the modified drift plains which form 

 the southern shores of Long Island, Martha's Vineyard, Nan- 

 tucket, and Cape Cod. A subsequent depression of the land 

 there, continuing perhaps to the present time, has brought the 

 sea into these old river courses. But north and northwest 

 from this line the land at the time of recession of the ice-sheet 

 was lower than now, and the coast and estuaries were more 

 submerged by the sea. At Boston and northward to Cape 

 Ann the depression appears to have been no more than 10 to 

 25 feet. Fossiliferous beds overlying the till show that the 

 vertical amount of the marine submergence in the vicinity of 

 Portsmouth was about 150 feet; along the coast of Maine, 

 from 150 to about 300 feet ; on the northwestern shore of 

 Nova Scotia, about 40 feet ; thence increasing westward to 

 about 200 feet in the basin of the Bay of Chaleurs, 375 feet in 



* James Geikie, Prehistoric Europe, chapters xx and xxi, 1881. Warren 

 Upham, " On the Cause of the Glacial Period," Am. Geologist, vol. vi, pp. 327- 

 339, Dec, 1890. 



