102 i?. E, Dodge — Pleistocene Fossils from 3fass. 



that the waters immediately at the close of the Glacial period 

 were warmer than at present. Of twenty-five species thus far 

 reported from the dredgings, many of which are the same as 

 in the Glacial drift, fourteen are distinctly southern in their 

 distribution, according to Mr. Upham. Thus, as far as we can 

 determine by the testimony of fossils, the ocean waters of Cape 

 Cod both immediately before the advance of the ice sheet and 

 just after the retreat were warmer than at present. Whether 

 these changes in temperature were due to the presence or 

 absence of melting glaciers in the neighboring oceanic waters 

 or whether they were due to slight oscillations of land, it is 

 difficult to determine. The existence of elevated shore lines 

 and fossiliferous clays to the north of Massachusetts Bay, 

 noted by Prof. Shaler and others, would seem to show that 

 the changes of temperature were due to oscillations of the 

 continent which at one time gave access to the warmer southern 

 waters into Massachusetts Bay, and at others shut them out 

 more than at present. 



Inasmuch as the direction of ice movement during the 

 drumlin-making stage must have been from a generally north- 

 westerly direction in this region, as shown by the strise, the 

 fragments of shells now found in the drumlins must have occu- 

 pied a position, at the beginning of the ice advance, some- 

 where to the northwest of the spot where they are now found, 

 otherwise they could not have been taken up and carried by 

 the ice in such a manner as to be deposited in their present 

 position. As I have already stated, all these species of fossils 

 but two are now found living in the waters of Massachusetts 

 Bay, and if the necessary conditions for their existence have 

 alw T ays been the same, it would appear that, at the time the 

 ice sheet overrode this portion of the coast, there must have 

 been somewhere in the western portion of Boston Harbor, 

 probably near the present estuary of the Charles River, an 

 extensive colony of shells of many different species. Yet we 

 find no evidence, other than the shells themselves, of the exist- 

 ence of any such colony of invertebrates, in the localities I 

 have noted. It would seem very strange however that all the 

 more important discoveries of pleistocene fossils from the drift 

 of this region have been from one drumlin, while the several 

 drumlins in the immediate vicinity have furnished but a very 

 few species. It is especially difficult to understand why we 

 find but four different species of fossils in the large drumlin, 

 called Grover's Cliff, about a mile to the northeast of Win- 

 throp Great Head, while Great Head itself has given us 

 twenty-three species. 



It would seem furthermore as if the distance of travel 

 which these fragments underwent must have been considerable, 



