FOSSIL MARINE SHELLS AND THEIR OCCURRENCES. 307 



Their Occurrence in the Drumlins near Boston. — Warren Upham and 

 others have discovered marine shells and fragments of shells in the 

 bowlder-clay hills called "drumlins" near Boston.* His list shows, 

 however, that the species are nearly all the same as those of the recent 

 period. Mr Upham explains the occurrence of these shells in the 

 drumlins by supposing that the ice of the glacial period ploughed up 

 certain marine beds inclosing them to the north and carried them for- 

 ward to form a portion of the material of these bowlder-clay hills. 



Their Occurrence in the Lata < 'lay and Saxicava Sands of New Brunswick. — 

 Marine shells of Pleistocene age were found by G. F. Matthew and the 

 writer a number of years ago in clays and sands on the coasts of the Bay 

 of Fundy and Baie des Chaleurs, which have been correlated with the 

 Leda clay and Saxicava sands of the Saint Lawrence valley. Lists of 

 these shells were published in the reports of the Geological Survey of 

 Canada, etc.f The height of the terraced deposits in which the shells 

 occur clearly establishes the conclusion that when the lower fossiliferous 

 portions were laid down the land stood from 180 to 220 feet lower than 

 it is at the present day ; and as the Leda clay and Saxicava sands con- 

 taining these shells have invariably been found overlying the bowlder- 

 clay, it is naturally inferred that their deposition began about the close 

 of the glacial period and occupied a distinct and separate interval of 

 Pleistocene time. 



The Height of the Land and the Mode of Deposition of the 



BoWLDER-OLAY. 



It is a view generally held by glacialists who have studied the Pleisto- 

 cene deposits and related phenomena of coast borders, especially within 

 the glaciated belt, that the land was subsiding during the period of 

 melting or retirement of the ice.'! The lower unstratified portion of the 

 bowlder-clay here was probably deposited during the greatest advance 

 of tin; hind-ice; this ice, as shown on a previous page, having extended 

 beyond Partridge island. It seems to have consisted mainly of sheets 

 flowing out from the Saint John and Kennebeckasis valleys which may 



♦Proceedings of the Boston Soe. of Nat. Hist., vol. xxvi, 1888. 



t Report of Progress, Geol. Surv. Canada, part EE, 1877-'78 ; Ann. Rep. Geol. Surv. Canada, vol. 1, 

 part GG, 1885. 



t;J. D. Dana, Am. Jour. Sei., third series, vol. ii, pp. 324-330; vol. v, pp. 198-211; vol. x, pp. 168-183, 

 400-438; vol. xxiv, pp. 98-104. .J. W. Dawson, Bull. Geol. Soc. of America, vol. i, p. 318; Acadian 

 Geology, supplementary note to fourth .•■lit ion, 1891, p. 7. C H. Hitchcoqk, Geology of New Hamp- 

 shire, vol. iii, p. 27k. Professor Hitchcock is, however, rather inclined to the view that it was the 

 sea and not the land which changed level. Warren Upham, Bull. Geol. Soc. of America, vol. i, pp. 

 , r >i;:j-.">c>7. G. IB Stone, Am. Jour. Sci., vol. xl, pp. 122-144. Robert Chalmers, Ann. Rep. Geol. Surv- 

 Canada, vol. iv, 1888-89, pp. 10, Un ; Canadian Naturalist, vol. x, p. 54. G. M. Dawson, Report of Prog, 

 ess, Geol. Surv. Canada, 1877-78, pp. 133-1536. 



