188 CHARLES DARWIN 



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 sea-shells. 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 Pata- 

 gonia, 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 fea- 

 tures 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 con- 

 ditions which favour the life of the larger quadrupeds were 

 lately co-extensive with the world: what those conditions 

 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 inroad 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 provinces 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 pas- 

 ture, which have since been overrun by thousands and hun- 

 dreds of thousands of the descendants of the stock intro- 

 duced by the Spaniards? Have the subsequently introduced 



