xi.] GEOLOGICAL REFORM. 213 



reasonings, &quot; that the existing state of things on the earth, life 

 on the earth all geological history showing continuity of life 

 must be limited within some such period of time as one hundred 

 million years &quot; (loc. cit. p. 25). 



The first inquiry which arises plainly is, has it ever been 

 denied that this period may be enough for the purposes of 

 geology ? 



The discussion of this question is greatly embarrassed by the 

 vagueness with which the assumed limit is, I will not say defined, 

 but indicated, &quot; some such period of past time as one hundred 

 million years.&quot; Now does this mean that it may have been two, 

 or three, or four hundred million years ? Because this really 

 makes all the difference. 1 



I presume that 100,000 feet may be taken as a full allowance 

 for the total thickness of stratified rocks containing traces of life ; 

 100,000 divided by 100,000,000 = O OOl. Consequently, the 

 deposit of 100,000 feet of stratified rock in 100,000,000 years 

 means that the deposit has taken place at the rate of TT5 V^ of a 

 foot, or, say, -^ of an inch, per annum. 



Well, I do not know that any one is prepared to maintain 

 that, even making all needful allowances, the stratified rocks 

 may not have been formed, on the average, at the rate of -^ of 

 an inch per annum. I suppose that if such could be shown to 

 be the limit of world-growth, we could put up with the allowance 

 without feeling that our speculations had undergone any revolu 

 tion. And perhaps, after all, the qualifying phrase &quot; some such 

 period &quot; may not necessitate the assumption of more than T J F or 

 2T r T2 f an i nc h f deposit per year, which, of course, would 

 give us still more ease and comfort. 



But, it may be said, that it is biology, and not geology, which 

 asks for so much time that the succession of life demands vast 

 intervals ; but this appears to me to be reasoning in a circle. 

 Biology takes her time from geology. The only reason we have 



1 Sir William Thomson implies (loc. cit. p. 16), that the precise time is 

 of no consequence : &quot; the principle is the same ; &quot; but, as the principle is 

 admitted, the whole discussion turns on its practical results. 



