162 EXPLANATIONS. 



late geological period." Here, then, is a piece 

 of the world undoubtedly younger, so to speak, 

 than most other portions are in their totality, 

 that is to say, it has been dry land for a 

 much less space of time, though one still con- 

 siderable. What are the organic productions of 

 this curious archipelago ? In the first place, they 

 are " mostly aboriginal creations, found nowhere 

 else," though with an affinity to those of America. 

 Many of them are even peculiar to particular 

 islands in the group. But the remarkable fact 

 bearing on the present inquiry is, that, excepting 

 a rat and a mouse on two of the islands, supposed 

 to have been imported by foreign vessels, there are 

 no mammals in the Galapagos. The leading terres- 

 trial animals are reptiles, and these exist in great 

 variety, and in some instances of extraordinary 

 size. Lizards and tortoises particularly abound. 

 There are also birds, eleven kinds of swimmers 

 and waders, and twenty-six purely terrestrial. 

 All this harmonizes with our ideas of the world in 

 general at the time of the oolites. It speaks of 

 time being necessary for the completion of the 

 animal series in any scene of its development. 

 The Galapagos have not had the full time required 

 for the completion of the series, and it is incom- 



