8 THE DARWINIAN HYPOTHESIS I 



isthmus of Panama. 1 Wherever we look, then, 

 living nature offers us riddles of difficult solution, 

 if we suppose that what we see is all that can 

 be known of it. 



But our knowledge of life is not confined to the 

 existing world. Whatever their minor differences, 

 geologists are agreed as to the vast thickness of the 

 accumulated strata which compose the visible part 

 of our earth, and the inconceivable immensity of 

 the time the lapse of which they are the imperfect 

 but the only accessible witnesses. Now, through- 

 out the greater part of this long series of stratified 

 rocks are scattered, sometimes very abundantly, 

 multitudes of organic remains, the fossilised 

 exuviae of animals and plants which lived and 

 died while the mud of which the rocks are formed 

 was yet soft ooze, and could receive and bury 

 them. It would be a great error to suppose that 

 these organic remains were fragmentary relics. 

 Our museums exhibit fossil shells of immeasurable 

 antiquity, as perfect as the day they were formed ; 

 whole skeletons without a limb disturbed ; nay, 

 the changed flesh, the developing embryos, and 

 even the very footsteps of primaeval organisms. 

 Thus the naturalist finds in the bowels of the earth 

 species as well defined as, and in some groups 

 of animals more numerous than, those which 

 breathe the upper air. But, singularly enough, 

 the majority of these entombed species are wholly 

 1 [See page 60 Note.] 



