CAUSES OF EXTINCTION. 223 



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 powei-, 

 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 sea-shells. 

 Since they lived, no very gi-eat 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 be- 

 lief of some great catastrophe ; but thus to destroy 

 animals, both large and small, in Southern Patago- 

 nia, 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 examina- 

 tion, moreover, of the geology of La Plata and Pata- 

 gonia, 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 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, temper- 

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

 In North America, we positively know from Mr. 

 Lyell that the large quadrupeds lived subsequent- 

 ly to that period when boulders were brought into 

 latitudes at which icebergs now never an-ive : 

 firom conclusive but indirect reasons we may feel 

 sure, that in the southern hemisphere the Macrau- 

 chenia also lived long subsequently to the ice- 

 transporting boulder-period. Did man, after his 



