98 



BAHIA BLANCA. 



Aug. 1833. 



we know that the mass could not have been accumulated on 

 the beach itself. At the present time^ part of the bed is 

 daily washed by the tide^ while another part has been raised 

 a few feet above the level of the sea. Hence we may infer, 

 that the elevation has here been trifling, since the period 

 when the mammalia, now extinct, were living. This con- 

 clusion is in harmony with several other considerations (such 

 as the recent character of the beds underlying the Pampas 

 deposit), but which I have not space in this work to 

 enter on. 



From the general structure of the coast of this part of 

 South America, we are compelled to believe, that the changes 

 of level have all (at least of late) been in one direction, and 

 that they have been very gradual. If, then, we look back 

 to the period when these quadrupeds lived, the land pro- 

 bably stood at a level, less elevated only by a few fathoms 

 than at present. Therefore, its general configuration since 

 that epoch cannot have been greatly modified ; a conclusion 

 which certainly would be drawn from the close similarity in 

 every respect, between the shells now living in the bay (as 

 well as in the case of the one terrestrial species) with those 

 which formerly lived there. 



The surrounding countr}^, as may have been gathered from 

 this journal, is of a very desert character. Trees nowhere 

 occur, and only a few bushes, which are chiefly confined to 

 depressions among the sand-hillocks, or to the borders of the 

 saline marshes. Here, then, is an apparent difiiculty : we 

 have the strongest evidence that there has occurred no great 

 physical change to modify the features of the country, yet 

 in former days, numerous large animals were supported on 

 the plains now covered by a thin and scanty vegetation. 



That large animals require a luxuriant vegetation, has been 

 a general assumption, which has passed from one work to 

 another. I do not hesitate, however, to say that it is com- 

 pletely false ; and that it has vitiated the reasoning of geolo- 

 gists, on some points of great interest in the ancient history 

 of the world. The prejudice has probably been derived 



