DARWIN AND THE ORIGIN OF SPECIES 243 



fuse the materials of which it is composed, provided it has 

 occupied its present position, or a similar position, in space. 

 The data for this calculation are still very imperfect, but the 

 result of analogous calculation applied to the sun, as worked out 

 by Professor Sir W. Thomson, is five hundred million years, and 

 the results derived from the observed temperatures of the earth 

 are of the same order of magnitude. This calculation is a mere 

 approximation. A better knowledge of the distribution of heat 

 in the interior of the globe may modify materially our estimates. 

 A better knowledge of the conducting powers of rocks, &c., for 

 heat, and their distribution in the earth, may modify it to a less 

 degree, but unless our information be wholly erroneous as to 

 the gradual increase of temperature as we descend towards the 

 centre of the earth, the main result of the calculation, that the 

 centre is gradually cooling, and if uninterfered with must, 

 within a limited time, have been in a state of complete fusion, 

 cannot be overthrown. Not only is the time limited, but it is 

 limited to periods utterly inadequate for the production of 

 species according to Darwin's views. We have seen a lecture- 

 room full of people titter when told that the world would not, 

 without supernatural interference, remain habitable for more 

 than one hundred million years. This period was to those people 

 ridiculously beyond anything in which they could take an 

 interest. Yet a thousand years is an historical period well 

 within our grasp as a Darwinian or geological unit it is almost 

 uselessly small. Darwin would probably admit that more than 

 a thousand times this period, or a million years, would be no 

 long time to ask for the production of a species differing only 

 slightly from the parent stock. We doubt whether a thousand 

 times more change than we have any reason to believe has taken 

 place in wild animals in historic times, would produce a cat from 

 a dog, or either from a common ancestor. If this be so, how 

 preposterously inadequate are a few hundred times this unit for 

 the action of the Darwinian theory ! 



But it may be said they are equally inadequate for the geo- 

 logical formations which we know of, and therefore your calcu- 

 lations are wrong. Let us see what conclusions the application 

 of the general theory of the gradual dissipation of energy would 

 lead to, as regards these geological formations. We may per- 



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