368 W. Zfpha/m — Marine Shells and Fragments 



Looking over the various lists of Pleistocene fossils found 

 on Gardiner's island and in Sankoty Head under the drift of 

 the last ice-sheet, in these drumlins of till near Boston, and in 

 the modified drift of the glacial recession thence northward to 

 Maine, ]STew Brunswick, and the valley of the St. Lawrence, 

 we cannot fail to be surprised that all these are still living in 

 the adjoining ocean to-day. So recent was the glacial period* 

 that none of them has become extinct, nor, with very rare ex- 

 ceptions, undergone any noteworthy change in form or size. 

 But the vicissitudes to which they were exposed during the last 

 of our two principal glacial epochs, when the ice-sheets east of 

 the Alleghenies advanced farther than in the earlier glaciation, 

 were doubtless well adapted to cause both extinctions and mod- 

 ifications of species. How vast then must be the duration of 

 the time occupied in the evolution of the complex faunas and 

 floras of our globe, and in the formation of all the fossilif erous 

 groups of rocks since the dawn of terrestrial life ! 



In various parts of Great Britain such transported Pleisto- 

 cene shells are found in the till, both in its low and smooth 

 tractsf and in its hilly and knolly terminal moraines traced by 

 Professor Lewis, as well as in the associated kames4 Some of 

 these fossiliferous glacial deposits occur in Ireland, northern 

 Wales and northwestern England at heights 1,100 to 1,350 feet 

 above the sea, and have been generally considered as proof of 

 marine submergence to that depth. Instead of this, Lewis has 

 shown§ that the shells and fragments of shells found there 

 were brought by the currents of the confluent ice-sheet which 

 flowed southward from Scotland and northern Ireland, passing 

 over the bottom of the Irish sea, there plowing up its marine 

 deposits and shells, and carrying them upward as glacial drift 

 to these elevations, so that they afford no testimony of the for- 

 mer subsidence of the land. This removes one of the most 

 perplexing questions that glacialists have encountered ; for no- 

 where else in the British Isles is there proof of any such sub- 

 mergence during or since the glacial period, the maximum 

 known being 510 feet near Airdrie in Lanarkshire, Scotland. | 

 At the same time the submergence on the southern coast of 

 England was only from 10 to 60 feet,T while no traces of raised 



* Compare Proceedings B. S. N. H., vol. xxiii, 188T, p. 446. 



\ Geikie's Great Ice Age, second ed., pp. 164-185, and 337-340. 



% Quart. Journ. Geol. Soc, vol. xxx, 1874, pp. 27-42; xxxiv, 1878, pp. 383-397; 

 xxxvi, 1880, pp. 351-5; xxxvii, 1881, pp. 351-369; and xliii, 1887, pp. 73-120; 

 also, Geological Magazine, II, vol. i, 1874, pp. 193-197. 



§ Report of the British Association for Adv. of Sci., Birmingham, 1886, pp. 

 632-635; Am. Naturalist, vol. xx, pp. 919-925, Nov., 1886; this Journal, III, 

 vol. xxxii, pp. 433-438, Dec, 1886. Also, see the American Geologist, vol. ii, pp. 

 371-379, Dec, 1888. 



|| Quart. Journ. Geol. Soc, vol. vi, 1850, pp. 386-8; xxi, 1865, pp. 219-221. 



\ Quart. Journ. Geol. Soc, xxxiv, 1878, pp. 454-7; xxxix, 1883, p. 54. Geol. 

 Mag., II, vol. ii, 1875, p. 229 ; II, vi, 1879, pp. 166-172. 



