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 @&tricts, 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.t 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. 
+ At Buenos Aires the alluvial deposit itself is called “tosca.” 
