A LAND OF SKELETONS 73 



been some kind of connection between the faunas of South 

 America and Australia. 



The country that has afforded the most information with 

 regard to the extinct fauna of South America is the Argen- 

 tine Republic, which includes not only Buenos Aires and 

 the adjacent provinces forming Argentine proper, but like- 

 wise the whole of Patagonia. Confining our attention, in 

 the first place, to the province of Buenos Aires and some 

 of the neighbouring districts, we may note that the greater 

 part of this vast tract of country is one boundless level 

 plain formed by an alluvial deposit of rich black mud 

 brought down from the higher lands of the interior by the 

 tributaries of the Rio de la Plata, and constituting the most 

 extensive pasture-land in the world. Near Buenos Aires 

 and the valley of the Rio de la Plata this alluvial deposit, 

 which in places alternates with sandy beds, is of immense 

 thickness ; * but farther to the south it thins out rapidly. 

 In some places in the neighbourhood of La Colina, about 

 a hundred miles from Bahia Blanca, for instance, the black 

 soil is not more than a couple of feet in thickness, and 

 is underlain by a hard white calcareous deposit, locally 

 known as " tosca," and much resembling some of the 

 deposits formed by hot springs.f That the black alluvial 

 deposit, which, from forming the whole of the Pampas, or 

 plain country, is known to geologists as the Pampean 

 formation, is of fresh-water origin is perfectly clear, and it 

 is probable that it was largely formed in marshes and 

 swamps, one of its most striking features being the total 

 absence of pebbles or stones. Indeed, throughout the 

 country, except in the neighbourhood of the mountains, 



* Near Buenos Aires it has been bored into for depths of fifty 

 and ninety feet. 



t At Buenos Aires the alluvial deposit itself is called "tosca." 



