THE DISCOVERER 9 1 



period, there was sufficient accord between them to 

 make the biologists feel themselves in a tight place. 

 Reckoning, from the rate at which materials, through 

 the agency of rivers, are being deposited on ocean- 

 bottoms, how long a time was necessary for the for- 

 mation of the sedimentary rocks, and of rocks pre- 

 sumably within the life-period, the aggregate thickness 

 of which is estimated at about fifty miles, they found 

 the years allowed by the mathematicians wholly insuf- 

 ficient. Darwin was much concerned. Writing to 

 Wallace in 1869, he says: "Thomson's views of 

 the recent age of the world have been for some time 

 one of my sorest troubles;" and again, in 1871, "I 

 can say nothing more about missing links than what I 

 have said. I should rely much on pre-Silurian times; 

 but then comes Sir W. Thomson, like an odious 

 spectre." Huxley was in no wise disturbed. 



Biology [he said] 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 

 persist through a series of deposits which, geology in- 

 forms 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 rapidity 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 



