A HISTORY OF SCIENCE 



both. In an arbitrary system we had surely no reason 

 to expect mammals after reptiles ; yet in this order they 

 came . The writer in the Edinburgh Review speaks of ani- 

 mals as coming in adaptation to conditions, but this is 

 only true in a limited sense. The groves which formed 

 the coal-beds might have been a fitting habitation for 

 reptiles, birds, and mammals, as such groves are at the 

 present day ; yet we see none of the last of these classes 

 and hardly any traces of the two first at that period of 

 the earth. Where the iguanodon lived the elephant 

 might have lived, but there was no elephant at that 

 time. The sea of the Lower Silurian era was capable 

 of supporting fish, but no fish existed. It hence forci- 

 bly appears that theatres of life must have remained un- 

 serviceable, or in the possession of a tenantry inferior to 

 what might have enjoyed them, for many ages: there surely 

 would have been no such waste allowed in a system 

 where Omnipotence was working upon the plan of 

 minute attention to specialities. The fact seems to 

 denote that the actual procedure of the peopling of the 

 earth was one of a natural kind, requiring a long space 

 of time for its evolution. In this supposition the long 

 existence of land without land animals, and more par- 

 ticularly without the noblest classes and orders, is only 

 analogous to the fact, not nearly enough present to the 

 minds of a civilized people, that to this day the bulk of 

 the earth is a waste as far as man is concerned. 



"Another startling objection is in the infinite local 

 variation of organic forms. Did the vegetable and 

 animal kingdoms consist of a definite number of species 

 adapted to peculiarities of soil and climate, and uni- 

 versally distributed, the fact would be in harmony with 



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