O 



542 



GEOGRAPHICAL DISTRIBUTION OF SPECIES. [Cii. XXXVIII. 



Mr. "Wallace^ very probably liave crossed the desert in the 

 tracks of caravans. If Ave confine onr attention to the 

 genera instead of species^ we find that ont of thirty-one only 

 three are common to the Palsearctic and Ethiopian regions. 



From wl 

 e submai 



(p. 562) of 



of Africa or Tangiers (a ridge twenty-two miles long and 

 from five to seven miles broad^ and nowhere covered by a 

 depth of water exceeding 220 fathoms), we learn that the 

 imion of Southern Europe with Africa does not imply a 



great change in the relative level of land and sea. 

 p-eoloerist at least is familiar with the fact that the 



b 



in 



The 



risnio^ 



and sinking of land and of the bed of the Mediterranean 

 within the Newer Pliocene Period has, in Sicily and else- 

 where, far exceeded the amount which would be required 

 to unite the coasts on the opposite side of the Straits of 

 Gibraltar, A change of level of about 70 fathoms would 

 unite Malta and Gozo with Sicily, and one of 200 fathoms 

 would join Malta to Tripoli by an isthmus 170 miles loi 

 A similar change would connect Italy with Sicily, and the 

 latter with Africa by the Adventure Bank. We can only 

 explain, by this and other analogous land communications of 

 modern geological date, the remarkable resemblance of the 

 fauna and flora of the islands of the Mediterranean and the 

 nearest mainland, notwithstanding the general depth of that 

 sea. Some of the mountainous islands, it is true, of the 

 Egean are inhabited by peculiar species of landshells, as was 

 ascertained by the late Edward Eorbes and Captain Spratt ; 

 but these mountains may perhaps have been insulated from 

 a remote period, as freshwater strata of Miocene age occur 

 in parts of them, and the surrounding sea is of vast depth. 

 The remains of the African elephant and of the Eleplio.^ 

 antiquusy and of an extinct hippopotamus in Sicily, and, 

 what is more wonderful, of several species of elephant, and 

 an hippopotamus in caverns in the small island of Malta, 

 bear testimony to great geographical changes in compara- 

 tively modern or Pliocene times. 



As to the distinctness above alluded to of the North- 

 African fauna from that south of the Sahara, we know that 



i 



