Geological Chronology. 23 



ure which natural forces employ in laying down a 

 stratum of clay on the bed of a river is certainly 

 not the same as the measure which divides the 

 story of mankind into days and years and centuries, 

 by solar and terrestrial revolutions. Nor is it the 

 same as that which marks off generation from gen- 

 eration among mankind, dividing them by the 

 births and deaths of men. Geology, in the order 

 and in the thickness of its deposits, agrees with 

 neither of these processes, neither that of astronomy 

 nor that of anthropology. If the astronomical 

 revolutions have been regular, if the revolving cy- 

 cles of human generations have been quite irregular, 

 the evolution of the earth's present surface has had 

 a measure of its own, a time of its own, not identi- 

 cal with either of theirs. Yet, to derive any light 

 from geology on the subject of man's antiquity, its 

 time must be made commensurate with man's time. 

 And accordingly the inductive effort has been made 

 to argue from what we see, in present circumstances, 

 going on in certain places that we know, to what 

 we have not seen, in circumstances and places en- 

 tirely different and unknown. But this inductive 

 effort is faulty, because there is no induction about 

 it. 



16. Induction, as a form of argument, requires a 

 sufficient enumeration of phenomena to 

 formulate a general law, which is found ^™on.° f 

 to stand the test of verification on be- 

 ing applied to cases known, and which, therefore, 



