74 TRAVELS IN BRAZIL. 



sent level of the Caspian sea, should be combined, 

 we think, with the opening of the strait of Gib- 

 raltar ; at least, there are not so many physical rea- 

 sons for believing that the strait was formed by the 

 ocean breaking through. It must be left to future 

 investigation, to determine whether a conformation 

 like that in the Mediterranean is found in other 

 great gulfs, for instance, that of Mexico, which it 

 in so many respects resembles. 



The formation of the mountains in the vicinity of 

 the town of Tarifa, agrees with that about Gibraltar ; 

 the limestone, however, is in thin strata, and the 

 slabs are therefore used for domestic purposes. On 

 the limestone lies a slaty bluish sandstone, of a finer 

 grain than that of St. Roque. On the most south- 

 ern point of the continent, which runs out from 

 the harbour, towards a small rocky island, on which 

 a tower is built, we observe a massy conglomerate 

 of rolled fragments of limestone, and remains of 

 still existing sea animals, such as cardium, myti- 

 lus, and the large flat edible Ostrea jacohcea (the 

 Mediterranean scallop), which are sometimes heap- 

 ed together in thick layers, united only by a little 

 stalactic limestone. There are also petrified alcy- 

 onia, corallines, sponges, madrepores, &c. in this 

 alluvial land, which has evident traces of a very 

 recent origin ; it appears to be constantiy on the 

 increase, as the sea daily brings a sufficient quantity 

 of marine animals, and calcareous cement. 



