III.] DISAPPEARANCE OF LARGE FORMS. 121 



its plains. With regard to this extraordinary, and apparently 

 sudden disappearance of almost all the larger forms of animal life 

 from South America, it may be pretty confidently asserted, from 

 the organisation of the creatures themselves, that at the time when 

 the ground-sloths flourished, extensive portions of what is now the 

 open pampas of Argentina were covered with forest ; and why the 

 whole district should have become practically treeless, seeing that 

 trees like the Australian eucalypti grow, when introduced, with 

 more vigour than in their native home, is exceedingly hard to 

 understand. That the country even when thus denuded was 

 unsuited to the needs of the larger forms of mammalian life, is, 

 however, negatived by the circumstance that in many parts the 

 horses and cattle introduced from Europe have run wild and 

 increased to an almost unprecedented extent. Neither does it 

 appear that the extermination can be attributed to a period of 

 extreme cold, since a glaciation of the pampas would assuredly 

 have left unmistakable evidence of its presence. It is likewise 

 practically certain that the clean sweep of the forests of Argentina 

 and the larger mammals of the whole of South America is not due 

 to the hand of man. It has, indeed, been suggested that the vast 

 herds of guanaco which formerly roamed the pampas may have 

 cleared the forests by preventing the growth of the seedlings ; but 

 when we recall the fact that numbers of this group of animals 

 flourished during the period when the alluvial formation was in the 

 course of being deposited, it scarcely looks as though this could 

 have been a vera causa. Moreover, if the forests were by some 

 means or other actually destroyed, and the extermination of their 

 animal denizens thus encompassed, there would still remain the 

 disappearance of plain-dwelling forms, like horses, to be accounted 

 for. Some have thought that pumas, by preying on the colts, 

 were the active agents in this instance ; but even if such were 

 really the case, it gives no help with regard to the disappearance 

 of the ground-sloths and glyptodonts; the latter being such 

 strongly armoured creatures that it is absolutely certain they were 

 not killed off by any animal foes. The problem is further com- 

 plicated by the circumstance that the fossil remains of nearly all 

 the larger animals which formerly inhabited the pampas are also 

 found in the caverns of Brazil, where the climate is now, and 



