X GEOLOGICAL KEFORM 329 



this appears to me to be reasoning in a circle. 

 Biology takes her time from geology. The only 

 reason we have for believing in the slow rate of 

 the change in living forms is the fact that they 

 jDcrsist through a series of deposits which, geology 

 informs us, have taken a long while to make. 

 If the geological clock is wrong, all the naturalist 

 will have to do is to modify his notions of the 

 -apidity of change accordingly. And I venture 

 to point out that, when we are told that the 

 limitation of the period during which living 

 beings have inhabited this planet to one, two, or 

 three hundred million years requires a complete 

 revolution in geological speculation, the onus 

 prchandi rests on the maker of the assertion, 

 who brings forward not a shadow of evidence 

 in its support. 



Thus, if we accept the limitation of time placed 

 before us by Sir W. Thomson, it is not obvious, 

 on the face of the matter, that we shall have to 

 alter, or reform, our ways in any appreciable 

 degree ; and we may therefore proceed with much 

 calmness, and indeed much indifference, as to the 

 result, to inquire whether that hmitation is 

 justified by the arguments employed in its 

 support. 



These argum_ents are three in number: — 

 I. The first is based upon the undoubted fact 

 that the tides tend to retard the rate of the 

 earth's rotation upon its axis. That this must 



