OF THE LEVEL OF THE SEA. 83 



marine shells discovered by him, found one which appears 

 to be extinct, and one which is not known as an inhabitant 

 of the British seas.* 



It appears that a similar proportion of recent and extinct 

 species is found to exist in the land and fresh-water shells 

 as amongst those of the sea. The labours of Messrs Strick- 

 land, Wood, Morris, and Brown, have thrown much light 

 upon the lacustrine and fluviatile deposits of this period. 

 Mr Strickland found in the gravel of the valley of the 

 Avon, amongst 24 species of shells, three which were extinct.*}* 

 Mr S. V. Wood in Suffolk, one extinct, Cyrena trigonula, 

 and two about which he was doubtful.^ Mr Brown dis- 

 covered one at Gosford in Essex ;§ and Mr Morris, in de- 

 scribing a fresh-water deposit at Grays in the same county, 

 observed, that though many of the shells are identical with 

 recent ones, some few species are certainly different. || Mak- 

 ing every allowance, therefore, for the chances of future dis- 

 covery, or for the difference of opinion of conchologists as 

 to species, we must admit that some change has taken 

 place in the testacea. A much greater one must, however, 

 have taken place amongst the mammalia of the same period, 

 of which by far the greatest number appear to have become 

 extinct. In Scotland, the remains of the elephant, the 

 stag, and the fallow deer,^| all probably of extinct species, 

 have been found in the diluvial drift or till, and in marl- 



* Silurian System, p. 533. 



"t Silurian System, p. 555 — Geol. Proc. vol. ii. p. 111. 



t Nat. Hist. Mag. vol. vii. p. 274. § lb. vol. ix. p. 431. 



|| lb. vol. ix. p. 264. 



H The elephant has been found in the till on the line of the Union 

 Canal, Wern. Mem. vol. iv. p. 58 ; in the parish of Kilsyth, (Stat. Acct. 

 vol. xviii. p. 233) ; at Kilmarnock, the remains of which are preserved in 

 the Andersonian Museum, Glasgow ; and at Kilmaurs, associated with 

 sea-shells, and with the horns of the deer and fallow-deer, all appa- 

 rently of extinct species, they are preserved in theHunterian Museum. 



