328 GEOLOGICAL REFORM x 



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 yoVcr f a ft> or, say, -^ of an 

 inch, per annum. 



Well, I do nofr know that any one is prepared 

 to maintain that, even making all needful allow- 

 ances, 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 revolution. 

 And perhaps, after all, the qualifying phrase 

 " some such period " may not necessitate the 

 assumption of more than T i^ or ^fo or irhr f 

 an inch of 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 



1 Sir William Thomson implies (loc. cit. p. 16) that the pre- 

 cise time is of no consequence : "the principle is the same " ; 

 but, as the principle is admitted, the whole discussion turns on 

 its practical results. 



