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SCIENCE. 



[N. S. Vol. IV. No. 96. 



no perceptible diflference of opinion as to 

 evolution itself, and this common ground 

 will bear the weight of all the zoological 

 arguments we shall consider to-day. 



It will be of interest to consider first how 

 the matter presented itself to naturalists 

 before the beginning of this controversy on 

 the age of this habitable earth. I will con- 

 tent myself with quotations from three 

 great writers on biological problems — men 

 of extremely different types of mind, who 

 yet agreed in their conclusions on this sub- 

 ject. 



In the original edition of the ' Origin of 

 Species ' (1859), Darwin, arguing from the 

 presence of trilobites, Nautilus, Lingula, etc., 

 in the earliest fossiliferous rocks, comes to 

 the following conclusion (pages 306, 307) : 

 " Consequently, if my theory be true, it is 

 indisputable that before the lowest Silurian 

 stratum was deposited long periods elapsed, 

 as long as, or probably far longer than, the 

 whole interval from the Silurian age to the 

 present day ; and that during these vast yet 

 quite unknown periods of time the world 

 swarmed with living creatures." 



The depth of his conviction in the validity 

 of this conclusion is seen in the fact that the 

 passage remains substantially the same in 

 later editions, in which, however, Cambrian 

 is substituted for Silurian, while the words 

 * yet quite unknown ' are omitted, as a con- 

 cession, no doubt, to Lord Kelvin's calcula- 

 tions, which he then proceeds to discuss, 

 admitting as possible a more rapid change 

 in organic life, induced by more violent 

 physical changes. * 



We know, however, that such concessions 

 troubled him much, and that he was really 

 giving up what his judgment still approved. 

 Thus he wrote to "Wallace on April li, 1869 : 

 " Thomson's views of the recent age of the 

 world have been for some time one of my 

 sorest troubles. * *= *" And again, on July 

 12, 1871, alluding to Mivart's criticisms, he 



* 6th ed., 1872, p. 286. 



says : '' I can say nothing more about miss- 

 ing 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's demands for time in order to 

 account for pre-Cambrian evolution, as he 

 conceived it, were far more extensive. Al- 

 though in 1869 he bade the naturalist stand 

 aside and take no part in the controversy, 

 he had nevertheless spoken as a naturalist 

 in 1862, when, at the close of another Anni- 

 versary address to the same Society, he 

 argued from the prevalence of persistent 

 types " that any admissible hypothesis of 

 progressive modification must be compati- 

 ble with persistence without progression 

 through indefinite periods ;" and then main- 

 tained that '' should such an hypothesis 

 eventually be proved to be true * * * the 

 conclusion will inevitably present itself that 

 the Paleozoic, MesozoiCjCainozoic faunae and 

 florae, taken together, bear somewhat the 

 same proportion to the whole series of liv- 

 ing beings which have occupied this globe 

 as the existing fauna and flora do to them." 



Herbert Spencer, in his article on ' Illogi- 

 cal Geology ' in the Universal Revieiv for 

 July, 1859,* uses these words : " Only the 

 last chapter of the earth's history has come 

 down to us. The many previous chapters, 

 stretching back to a time immeasurably re- 

 mote, have been burnt, and with them all 

 the records of life we may presume they 

 contained." Indeed, so brief and unimpor- 

 tant does Herbert Spencer consider this last 

 chapter to have been that he is puzzled to 

 account for ' such evidences of progression 

 as exist ; ' and finally concludes that they 

 are of no significance in relation to the doc- 

 trine of evolution, but probably represent 

 the succession of forms by which a newly 

 upheaved land would be peopled. He ar- 

 gues that the earliest immigrants would be 



* Reprinted in Ms Essays, 1868, Vol. I., pp. 324- 

 376. 



