GEOLOGY AND EVOLUTION. 367 



of the evolutionist are manifold in number and variety. Our 

 study of "missing links" has already shown us that one special 

 phase of geological inquiry relates to the existence in the fossil 

 record of those forms which may be described as intermediate 

 in nature between existing species. If we suppose that no such 

 forms had been known to exist, we can conceive that whilst their 

 absence would not absolutely have negatived the theory of evolution, 

 the want of such evidence would have decidedly weakened the 

 evolutionist's case. The fulness with which the gaps have been 

 supplied with even a relatively limited search in geological directions, 

 has more than satisfied the evolutionist of the correctness of his 

 deductions respecting the existence of the transitional forms he would 

 expect the life of past seons to have exhibited. A second phase ef 

 geological inquiry in relation to the theory of descent is found in the 

 question of past time and its duration. The objection has naturally 

 been urged, that, if " natural selection " has operated in the past by 

 the production of minute variations, acting through periods of im- 

 mense antiquity, the drafts which the- evolutionist is compelled to 

 make on the bank of time are so great that collapse of the theory is 

 the result. Physicists of the highest eminence have formulated 

 opinions, based on apparently stable data, regarding the age of our 

 planet. It has accordingly been urged that, assuming the most ex- 

 tended antiquity which such opinions allow, there yet remains a 

 deficit in the age of the earth, compared with the demands or with 

 the expectations of the evolutionist. But to all such speculations 

 and considerations there remains one sufficient answer. So long as 

 we are comparatively ignorant of the exact factors to which the work 

 of evolution is due, it is idle to speculate on the time required for 

 the change and modification of species. That specific change may 

 have occasionally been more rapid in past ages than at present, is an 

 idea for which there is considerable justification to be found in the 

 history of the living beings we are able to study. Again, with im- 

 perfect knowledge of the progress and succession of climatal and 

 other changes in the past, and with but shadowy ideas regarding 

 the possibilities of biological change to-day, we have ample reason 

 to regard the relations of time past to evolution, as by no means so 

 simple as certain opinions would appear to indicate. The evidence 

 of geology itself, whilst rejecting the ancient ideas of" catastrophism " 

 and of sudden, cataclysmal changes, nevertheless must be held as 

 proving that cosmical and physical actions have not always presented 

 the phases we see exemplified before our eyes to-day. In a word, 

 until we have at hand fuller evidence regarding the manifest inter- 

 action between cosmical alteration and biological change between 

 physical revolutions and their effect upon the life of our globe all 

 speculations concerning the duration of time past in its relation to 



