THE CENTURY'S PROGRESS IN PALEONTOLOGY 



admitted, then Smith's view that there have been suc- 

 cessive rotations of population could no longer be denied. 

 Nor could it be in doubt that the successive faunas, whose 

 individual remains have been preserved in myriads, rep- 

 resenting extinct species by thousands and tens of thou- 

 sands, must have required vast periods of time for the 

 production and growth of their countless generations. 



As these facts came to be generally known, and as it 

 came to be understood in addition that the very matrix 

 of the rock in which fossils are embedded is in many 

 cases itself one gigantic fossil, composed of the remains 

 of microscopic forms of life, common-sense, which, after 

 all, is the final tribunal, came to the aid of belabored 

 science. It was conceded that the only tenable inter- 

 pretation of the record in the rocks is that numerous 

 populations of creatures, distinct from one another and 

 from present forms, have risen and passed away; and 

 that the geologic ages in which these creatures lived 

 were of inconceivable length. The rank and file came 

 thus, with the aid of fossil records, to realize the import 

 of an idea which James Hutton, and here and there 

 another thinker, had conceived with the swift intuition 

 of genius long before the science of paleontology came 

 into existence. The Huttonian proposition that time is 

 long had been abundantly established, and by about the 

 close of the first third of our century geologists had 

 begun to speak of "ages" and "untold asons of time" 

 with a familiarity which their predecessors had reserved 

 for days and decades. 



in 



And now a new question pressed for solution. If the 

 earth has been inhabited by successive populations of 

 G 97 



