OF THE LEVEL OF THE SEA. 75 



Amongst the fresh-water fossil shells, Mr Sowerby has ob- 

 served, that the Cyrena Trigonula* resembles one from 

 the Canal of Alexandria, and another resembles the Unio 

 Littoralis,^- a recent shell from Auvergne; he has, however, 

 pointed out differences which shew that they are not of the 

 same species, and therefore furnish no evidence respecting 

 climate. Mr Murchison has also found two extinct shells, 

 an Oliva and Bulla Ampulla, which he thinks give indica- 

 tions of a warm climate.;]; But as the Oliva has not been 

 identified with any recent species ; the same observation 

 applies to it as to the Unio and Cyrena.^ The Bulla Am- 

 pullaoccurs in the Indian Seas; but, according to Deshayes,|| 

 it is also to be found in the European Seas. The prepon- 

 derance of evidence is therefore clearly in favour of the 

 supposition that the climate was, if any thing, colder than it 

 is at present. It appears to me that we have similar evi- 

 dence respecting that of Sicily during the newer pliocene pe- 

 riod. According to Dr Phillippi,*f| out of ten of the fossil 

 shells which still exist in a recent state, but not in the Me- 

 diterranean, there is one which belongs to the Red Sea, all 

 the others are to be found in the more northern parts of 

 Europe. According to Deshayes** twenty-seven belong to 

 a northern, and three to a southern latitude. Slight altera- 

 tions of climate are easily explained ; there is ample proof 

 of extensive changes of level having taken place in America 



* Figured and described, Nat. Hist. Mag. vol. vii. p. 275 ; also in 

 LyelPs Elements of Geology, p. 60, fig. 24. 



f The recent shell is figured in Lyell's Elements, p. 61, fig. 27. The 

 fossil in the Nat. Hist. Mag., Oct. 1838, p. 548. 



t Silurian System, p. 534. 



§ See note on this shell in catalogue. 



II Vide Tables of Tertiary Shells, appended to Lyell's Geology, vol. 

 iii. 1st edition, p. 18. 



If Enumeratio Molluscorum Sicilise, 4to, Ber. 1836. 



** Tables of Tertiary Shells. 



