20-i IF. JJpham — Recent Fossils near Boston. 



extend to the Arctic Ocean, but including one found only on 

 the coast of New England, range to southward limits beyond 

 Cape Cod. In short, the temperature of the sea in Massachu- 

 setts Bay and in the estuaries of its rivers, at the time repre- 

 sented by these deposits, was evidently like that of the sea 

 now on the southern coast of New England, which, besides 

 the increase of the sun's heat due to the lower latitude, re- 

 ceives some contribution from the warmth of the Gulf Stream, 

 whereas the waters of the Gulf of Maine and Massachusetts 

 Bay are chilled by a coastal current from the north. 



The relative heights of land and sea were apparently almost 

 the same as now. Every, one of the twenty-five recorded 

 species flourishes on the shore between the levels of high and 

 low tide, or at the plane of extreme low tide, or in shallow 

 water of a few fathoms. In the list of each locality are 

 species that prefer a depth slightly below the lowest tide, and 

 each also has other species that are chiefly restricted to the 

 shore above low water mark. Probably the best interpretation 

 is that suggested by the layer of peat at the first locality, im- 

 mediately overlying the fossils, near the low tide level. The 

 water there was gradually becoming shallower, and the land 

 was finally lifted above the reach of the tide at the time of 

 formation of the peat. Subsequently it has been depressed at 

 least several feet, which latest movement has now apparently 

 ceased on this part of the coast. 



Postglacial oscillations of considerable amount, thus lifting the 

 land and afterward depressing it, are known to have affected 

 a large part of our Atlantic seaboard ; and Prof. A. E. Ver- 

 rill* and Sir William Dawsonf believe that these recent 

 changes of level have been sufficient to explain the important 

 changes of temperature of the sea here, whereby southern 

 mollusks were permitted to extend northward to the Gulf of 

 St. Lawrence but have since been exterminated, excepting 

 isolated colonies, north of Cape Cod and Massachusetts Bay. 

 Both these authors are inclined to attribute the northward ex- 

 tension of the southern fauna to a recent time of greater eleva- 

 tion of our coast, which is abundantly attested to a certain 

 amount, ranging from 10 to at least 40 feet,;}; by stumps of 

 forests, rooted where they grew, and by peat bogs, now found 

 submerged by the sea at many places along all the dis- 

 tance from New Jersey to Newfoundland. Professor Verrill 



*Tkis Journal, III, vol. vii, pp. 134-8, Feb., 1874. 



f Acadian Geology, Third edition, with Supplement, 1878. 



\ According to Sir William Dawson, 1. c, p. 31. Since this paper was prepared, 

 the author finds that Mr. Robert Chalmers reports a peat bed under the Tantramar 

 salt marsh at the head of the Bay of Fundy, about 80 feet below the present high 

 tide level (Annual Report of the Geological and Natural History Survey of Canada, 

 new series, vol. iv, for 1888-89, pp. 42 A and 10 N). 



