June 30, 1899.] 



SCIENCE. 



891 



ciples of Hutton, Playfair and Lyell than 

 of their opponents. But such is the free- 

 dom and the diversity of belief, of attitude 

 and of method, among geologists that as a 

 class they cannot be placed either here or 

 there in the schools, nor could they thirty- 

 five j'ears ago. 



But we are not primarily concerned with 

 these matters of the schools and of the 

 past. The address presses upon our atten- 

 tion matters of present interest and of pro- 

 found importance. Referring to his former 

 wide-ranged estimate of the time of the 

 consolidation of the earth, Lord Kelvin 

 says that " we now have good reason for 

 judging that it was more than twenty and 

 less than forty million j'ears ago, and prob- 

 ably much nearer twenty than forty (This 

 JoDRNAL, May 12, p. 27 1_), and he gives 

 qualified approval to Clarence King's esti- 

 mate of twenty-four million years. In the 

 course of the address he speaks of ' strict 

 limitations,' of 'sure assumption,' of 'cer- 

 tain truth,' and of ' no other possible alter- 

 native ; ' he speaks of ' one year after freez- 

 ing,' and even of ' half an hour after the 

 solidification ' ; he speaks of ' a crust of 

 primeval granite,' of a depth of ' several 

 centimeters,' and of other details of dimen- 

 sion and of time and of certitude so spe- 

 cifically and so confidently that it must en- 

 courage, in the average reader, the impres- 

 sion that the history of the earth is already 

 passing into a precise science through the 

 good offices of physical deduction. Is this 

 really true? Can the uninstructed layman 

 or the young geologist safely repose confi- 

 dence in these or any other chronological 

 conclusions as determinate ? Can these def- 

 inite statements, bearing so much the air of 

 irrefutable truth, be allowed to pass without 

 challenge ? What is their real nature and 

 their true degree of certitude when tested 

 respecting their fundamental postulates and 

 their basal assumptions ? 



With admirable frankness Lord Kelvin 



says (This Journal, May 12, p. 672) : " All 

 these reckonings of the history of under- 

 ground heat, the details of which I am sure 

 you do not wish me to put before you at 

 present, are founded on the very sure as- 

 sumption that the material of our present 

 solid earth all round its surface was at one 

 time a white-hot liquid." It is here can- 

 didly revealed that the most essential factor 

 in his reasonings rests ultimately upon an 

 assumption, an assumption which, to be sure, 

 he regards as ' very sure,' but still an as- 

 sumption. The alternatives to this assump- 

 tion are not considered. The method of 

 multiple working hypotheses, which is pe- 

 culiarly imperative when assumptions are 

 involved, is quite ignored. I beg leave to 

 challenge the certitude of this assumption 

 of a white-hot liquid earth, current as it is 

 among geologists, alike with astronomers 

 and physicists. Though but an understu- 

 dent of physics, I venture to challenge it on 

 the basis of physical laws and physical 

 antecedents. 



By way of preface it may be remarked 

 that the postulate of a white-hot liquid 

 earth does not rest on any conclusive geolog- 

 ical evidence, however generally it may be 

 entertained as a probable hypothesis. Stu- 

 dents of the oldest known rocks are not yet 

 agreed that these are all igneous even. But 

 granting that they may be all either igneous 

 or pyroclastic, there is a wide logical gap be- 

 tween this admission and the postulate that 

 they were all liquid at one time and enveloped 

 the whole earth. Looking quite in the op- 

 posite direction is the testimony of the 

 complex structure and intricate combination 

 of rocks, diverse at once in chemical, min- 

 eralogical and structural characters, which 

 the basement complex presents. The rela- 

 tions of the great batholite-like masses to 

 the enveloping foliated rocks, and of analo- 

 gous combinations of intrusive aspect, im- 

 ply the presence of a portion of the basement 

 complex in the already solid state when 



