178 EXTERryriNATION OF SPECIES, [ch 



allied races. If Buifon had known of the gigantic sloth 

 and armadillo-like animals, and of the lost Pachydermata^ 

 he might have said with a greater semblance of truth 

 that the creative force in America had lost its power, 

 rather than that it had never possessed great vigour. 

 The greater number, if not all, of these extinct quadrupeds 

 lived at a late period, and were the contemporaries of most 

 of the existing seashells. Since they lived, no very great 

 change in the form of the land can have taken place. 

 What, then, has exterminated so many species and whole 

 genera? The mind at first is irresistibly hurried into 

 the belief of some great catastrophe ; but thus to destroy 

 animals, both large and small, in Southern Patagonia, in 

 Brazil, on the Cordillera of Peru, in North America up to 

 Behring's Straits, we must shake the entire framework 

 of the globe. An examination, moreover, of the geology 

 of La Plata and Patagonia, leads to the belief that all the 

 features of the land result from slow and gradual changes. 

 It appears from the character of the fossils in Europe, Asia, 

 Australia, and in North and South America, that those 

 conditions which favour the life of the larger quadrupeds 

 were lately co-extensive with the world : what those con- 

 ditions were, no one has yet even conjectured. It could 

 hardly have been a change of temperature, which at about 

 the same time destroyed the inhabitants of tropical, 

 temperate, and arctic latitudes on both sides of the globe. 

 In North America we positively know from Mr. Lyell, 

 that the large quadrupeds lived subsequently to that period 

 when boulders were brought into latitudes at which icebergs 

 now never arrive : from conclusive but indirect reasons we 

 may feel sure, that in the southern hemisphere the 

 macrauchenia, also, lived long subsequently to the ice- 

 transporting boulder-period. Did man, after his first in- 

 road into South America, destroy, as has been suggested, 

 the unwieldy megatherium and the other Edentata? We 

 must at least look to some other cause for the destruction 

 of the little tucutuco at Bahia Blanca, and of the many 

 fossil mice and other small quadrupeds in Brazil. No one 

 will imagine that a drought, even far severer than those 

 which cause such losses in the province of La Plata, could 

 destroy every individual of every species from Southern 

 Patagonia to Behring's Straits. What shall we say of 

 the extinction of the horse ? Did those plains fail of 

 pasture, which have since been overrun by thousands and 



