chap. Tin. Elevation of Bahia B lancet. 193 



southward of Buenos Ayres, which M. d'Orbigny attri- 

 butes with much probability to the action of the sea, 

 before the plains were raised above its level. 1 



Soutlnvard of the Plata. — The coast as far as Bahia 

 Blanca (in lat. 39° S.) is formed either of a horizontal 

 range of cliffs, or of immense accumulations of sand- 

 dunes. Within Bahia Blanca, a small piece of table- 

 land, about twenty feet above high-water mark, called 

 Punt a Alta, is formed of strata of cemented gravel and 

 of red earthy mud, abounding with shells (with others 

 lying loose on the surface), and the bones of extinct 

 mammifers. These shells, twenty in number, together 

 with a Balanus and two corals, are all recent species, 

 still inhabiting the neighbouring seas. They will be 

 enumerated in the eleventh Chapter, when describing 

 the Pampean formation; five of them are identical 

 with the upraised ones from near Buenos Ayres. The 

 northern shore of Bahia Blanca is, in main part, formed 



1 Before proceeding to the districts southward of La Plata, it may 

 be worth while just to state, that there is some evidence that the 

 coast of Brazil has participated in a small amount of elevation. Mr. 

 Burchell informs me, that he collected at Santos (lat. 24° S.) oyster- 

 shells, apparently recent, some miles from the shore, and quite above 

 the tidal action. Westward of Bio de Janeiro, Capt. Elliot is asserted 

 (see Harlan, ' Med. and Phys. Res.,' p. 35, and Dr. Meigs, in ' Trans. 

 Amer. Phil. Soc.'), to have found human bones, encrusted with sea- 

 shells, between iifteen and twenty feet above the level of the sea. 

 Between Bio de Janeiro and Cape Frio I crossed sandy tracts 

 abounding with sea-shells, at the distance of a league from the coast; 

 but whether these tracts have been formed by upheaval, or through 

 the mere accumulation of drift sand, I am not prepared to assert. 

 At Bahia (lat. 13° S.), in some parts near the coast, there are traces 

 of sea-action at the height of about twenty feet above its present 

 level ; there are also, in many parts, remnants of beds of sandstone 

 and conglomerate with numerous recent shells, raised a little above 

 the sea-level. I may add, that at the head of Bahia bay there is a 

 formation, about forty feet in thickness, containing tertiary shells 

 apparently of fresh- water origin, now washed by the sea and en- 

 crusted with Balani ; this appears to indicate a small amount of 

 subsidence subsequent to its deposition. At Pernambuco (lat. 8° 

 S.), in the alluvial or tertiary cliffs, surrounding the low land on 

 which the city stands, I looked in vain for organic remains, or other 

 evidence of changes in level. 



