78 MOSTLY MAMMALS 
of their preservation is sufficiently accounted for by the 
nature of the deposit itself. The marvel, however, is in 
regard to the total disappearance of the whole of the larger 
forms and the reduction of the fauna of the Pampas to its 
present condition, together with the concomitant loss of 
the forests. It is not that the country is unsuited at the 
present day to the existence of the larger types of animal 
life, as witness the countless herds of horses and cattle 
with which its plains are now covered, together with the 
luxuriance and rapidity with which many kinds of trees 
flourish when introduced. Neither, I think, can it be due 
to a glacial epoch (although there appears to be evidence 
of the prevalence of a cold period in Patagonia), since any 
glaciation of the Pampas would have assuredly removed the 
greater part of the alluvial formation, besides having left 
indisputable evidence of its presence. Man can scarcely 
be credited with the extinction of either the fauna or the 
flora. It has been suggested that the number of guanaco 
with which the country was overrun previous to European 
settlement may have caused the destruction of the forests ; 
but we must remember that similar animals existed in 
greater variety during the Pampean period, while even if 
the disappearance of trees were due to their agency, this 
would have had no effect on plain-loving forms like horses. 
That the disappearance of the latter animals may have been 
due to the number of pumas is another suggestion, but it 
will be obvious that this could have had nothing to do with 
the destruction of gigantic creatures like the glyptodons 
and ground-sloths. The problem is further complicated 
by the circumstance that the remains of many of these 
creatures occur in caverns in the interior of Brazil, where 
the climate is still, and probably always has been, tropical. 
It would seem, therefore, that we must be content to regard 
