Beviews — Sir W. Thomsoris Geological Dynamics. 473 



Professor Huxley asked whether it had ever been denied that the 

 period to which Sir W. Thomson restricted geological time may be 

 enough for the purpose of geology, and remarked that on him rested 

 the onus probancli of his call for reformation. Accordingly Sir W. 

 Thomson now brings forward evidence to support his statement, 

 consisting of several passages from the works of Darwin, Jukes, and 

 Page, wherein the necessity of unlimited time is taught. On the 

 other hand, he quotes Professor Phillips' careful estimate of 

 96,000,000 years for the antiquity of the base of the stratified rocks, 

 which agrees so remarkably with his own conclusions, and also 

 quotes Mr. A. Greikie, who lately declared his opinion that all the 

 erosion of which we have monumental evidence in stratified rocks, 

 and in the shapes of hills and valleys over the world, could have 

 taken place several times over in the period of a hundred million 

 years. 



Professor Haughton, whilst admitting Sir W. Thomson's re- 

 striction of time, expresses his belief " that the time during which 

 organic life has existed on the earth is practically infinite, because it 

 can be shown to be so great as to be inconceivable by beings of our 

 limited intelligence," and, bearing this in mind, we do not see any- 

 thing objectionable in the following passage from Darwin, which is 

 quoted by Sir W. Thomson : — he who " does not admit how incom- 

 prehensibly vast have been the past periods of time may at once close 

 this volume." Sir W. Thomson denies that he took Uniformitarian- 

 ism to be the representative of geological speculation in general, he 

 attacked it, but he did not attack geological speculation in general. 

 The Evolutionism of which Prof. Huxley approves, he " always 

 considered to be the substantial and irrefragable part of geological 

 speculation." 



Prof. Huxley doubted whether any geologist at the present day 

 would be found to maintain absolute Uniformitarianism, to deny 

 that the rapidity of the rotation of the earth may be diminishing, 

 that the sun may be waxing dim, or that the earth itself may be 

 cooling, and expressed the opinion that, true or fictitious, they have 

 made no practical difference to the earth, during the period of 

 which a record is preserved in stratified deposits. 



Sir W. Thomson asks on what calculation this opinion is founded, 

 and adds that: — ''Fourier's theory of the conduction of heat 

 renders it almost impossible to escape the conclusion that, if the 

 earth has been solid and habitable continuously during the last 

 60 million years, its rate of increase of miderground temperature per 

 metre downwards must have been very sensibly more rapid 50 

 million years ago than now. The more recently discovered laws of 

 thermodynamics render it certain that the sun must have been 

 something very different 50 million years ago from what he is now ; 

 and almost certain that he must have been then very much hotter. 



" There is," he continues, " surely good ground for Sir Eoderick 

 Murchison's opinion that metamorphic causes have been more active 

 in ancient times than at present, because of more rapid augmenta- 

 tion of temperature downwards below the earth's surface ; and it 



