CHAP. VII.] MAMMALIA OF THE NEW WORLD. 143 



always more or less united to the tropical areas; "while the 

 evidence of the extinct mammalia themselves shows, that South 

 America has been for the most part isolated from the northern 

 continent, and did not take part in the development of its 

 characteristic Tertiary fauna. 



Before speculating further on this subject, it will be well to 

 lay before our readers a summary of South American paleon- 

 tology, after which we shall be in a better position to draw 

 correct inferences from the whole body of the evidence. 



South Amepjca. 



Unfortunately, our knowledge of the interesting fossil fauna 

 of this continent, is almost wholly confined to the Post-Pliocene 

 and Pliocene periods. A few remains have been discovered in 

 deposits believed to be of Eocene age, but nothing whatever 

 representing the vast intervening period, so rich in peculiar 

 forms of animal life both in Xortli America and Europe. 



Fauna of the Brazilian caves. — AYhat we know of the Post- 

 Pliocene period is chiefly due to the long-continued researches 

 of Dr. Lund in the caves of Central Brazil, mostly situated in 

 a district near the head waters of the San Francisco river 

 in the Province of Minas Geraes. The caves are formed in 

 limestone rocks, and are so numerous that Dr. Lund visited 

 thousands, but only sixty contained bones in any quantity. 

 These caves have a floor of reddish earth, often crowded with 

 bones. In one experiment, half a cubic foot of this earth 

 contained jaws of 400 opossums, 2,000 mice, besides remains 

 of bats, porcupines and small birds. In another trial, the 

 whole of the earth in a cavern was carried out for examin- 

 ation, amounting to 6,552 firkins ; and, from a calculation 

 made by measured samples, it was estimated to contain 

 nearly seven millions of jaw-bones of cavies, opossums, por- 

 cupines, and mice, besides small birds, lizards, and frogs. This 

 immense accumulation is believed to have been formed from 

 the bodies of animals brought into the cavern by owls ; and, 

 as these are unsocial birds, the quantity found implies an 



