OCTOBEE 30, 1896.] 



SCIENCE. 



629 



the lower forms of animal and vegetable 

 life, and that these would be followed by an 

 irregular succession of higher and higher 

 form.s, which ' would thus simulate the suc- 

 cession presented by our own sedimentary 

 series.' 



We see, then, what these three great 

 writers on evolution thought on this sub- 

 ject ; they are all convinced that the time 

 during which the geologists concluded that 

 the fossiliferous rocks had been formed was 

 utterly insufficient to account for organic 

 evolution. 



Our object to-day is first to consider the 

 objections raised by physicists against the 

 time demanded by the geologist, and still 

 more against its multiplication by the stu- 

 dent of organic evolution ; secondly, to in- 

 quire whether the present state of paleon- 

 tological and zoological knotvledge increases 

 or diminishes the weight of the threefold 

 opinion quoted above — an opinion formed 

 on far more slender evidence than that 

 which is now available. And if we find 

 this opinion sustained, it must be considered 

 to have a very important bearing upon the 

 controversy. 



The arguments of the physicists are three: 



First, the argument from the observed sec- 

 ular change in the length of the day,the most 

 important element of which is due to tidal 

 retardation. It has been known for a very 

 long time that the tides are slowly increas- 

 ing the length of our day. Huxley explains 

 the reason with his usual lucidity: '' That 

 this must be so is obvious, if one considers, 

 roughly, that the tides result from the pull 

 which the sun and moon exert upon the 

 sea, causing it to act as a sort of brake upon 

 the solid earth."* 



A liquid earth takes a shape which fol- 

 lows from its rate of revolution, and from 

 which, therefore, its rate of revolution can 

 be calculated. 



The liquid earth consolidated in the form 



*Anniv. Address to Geol. Soc, 1869. 



it last assumed, and this shape has per- 

 sisted until now and informs us of the rate 

 of revolution at the time of consolidation. 

 Comparing this with the present rate, and 

 knowing the amount of lengthening in a 

 given time due to tidal friction, we can cal- 

 culate the date of consolidation as certainly 

 less than 1,000 million years ago. 



This argument is fallacious, as many 

 mathematicians have shown. The present 

 shape tells us nothing of the length of the 

 day at the date of consolidation; for the 

 earth, even when solid, will alter its form 

 when exposed for a long time to the action 

 of great forces. As Professor Perry said in 

 a letter to Professor Tait :* "I know that 

 solid rock is not like cobbler's wax, but 

 1,000 million years is a very long time, and 

 the forces are great." Furthermore, we 

 know that the earth is always altering its 

 shape and that whole coastlines are slowly 

 rising or falling, and that this has been 

 true, at any rate, during the formation of 

 the stratified rocks. 



This argument is dead and gone. We 

 are, indeed, tempted to wonder that the 

 physicist, who was looking about for argu- 

 ments by which to revise what he con- 

 ceived to be the hasty conclusions of the 

 geologists as to the age of the earth, should 

 have exposed himself to such an obvious 

 retort in basing his own conclusions as to 

 its age on the assumption that the earth, 

 which we know to be always changing in 

 shape, has been unable to alter its equa- 

 torial radius by a few miles under the ac- 

 tion of tremendous forces constantly tend- 

 ing to alter it, and having 1,000 million 

 years in which to do the work. 



With this flaw in the case it is hardly 

 necessai-y to insist on our great uncertainty 

 as to the rate at which the tides are length- 

 ening the day. 



The spectacle presented by the geologist 

 and biologist, deeply shocked at Lord Kel- 



* Nature, January 3, 1895. 



