May 12, 1899.] 



SCIENCE. 



671 



conceivably ' great vista of past time, or 

 even a few thousand million years, for the 

 historj' of life on the earth, and approximate 

 uniformity of plutonic action throughout 

 that time; which, as we have seen, was 

 verj' generally prevalent thirty years ago, 

 among British Geologists and Biologists ; 

 and which, I must say, some of our chiefs 

 of the present day have not yet abandoned. 

 Witness the Presidents of the Geological 

 and Zoological Sections of the British As- 

 sociation at its meetings of 1893 (Notting- 

 ham), and of 1896 (Liverpool): 



Sir. Teall : Presidential Address to the Geological 

 Section, 1893, " Tlie good old British ship 'Unifor- 

 mity,' built by Hutton and refitted by Lyell, has won 

 so many glorious victories in the past, and appears 

 still to be in such excellent fighting trim, that I see 

 no reason why she should haul down her colors either 

 to ' Catastrophe ' or ' Evolution. ' Instead, therefore, 

 of acceding to the request to ' hurry up ' we make a 

 demand for more time." 



Professor Poultou : Presidential Address to the 

 Zoological Section, 1896. "Our argument does not 

 deal with the time required for the origin of life, or 

 for the development of the lowest beings with which 

 we are acquainted from the first formed beings, of 

 which we know nothing. Both these processes may 

 have required an immensity of time; but as we 

 know nothing whatever about them and have as 

 yet no prospect of acquiring any information, we 

 are compelled to confine ourselves to as much of 

 the process of evolution as we can infer from the 

 structure of living and fossil forms — that is, as re- 

 gards animals, to the development of the simplest 

 into the most complex Protozoa, the evolution of the 

 IMetazoa from the Protozoa, and the branching of the 

 former into its numerous Phyla, with all their Classes, 

 Orders, Families, Genera, and Species. But we shall 

 find that this is quite enough to necessitate a very 

 large increase in the time estimated by the geologist." 



§ 15. In my own short paper from which 

 I have read you a sentence, the rate at 

 which heat is at the present time lost from 

 the earth by conduction outwards through 

 the upper crust, as proved by observations 

 of underground temperature in different 

 parts of the world, and by measurement of 

 the thermal conductivity of surface rocks 

 and strata, sufficed to utterly refute the 



Doctrine of Uniformity as taught by Hut- 

 ton, Lyell, and their followers ; which was 

 the sole object of that paper. 



§ 16. In an earlier communication to the 

 Eoyal Society of Edinburgh, * I had con- 

 sidered the cooling of the earth due to this 

 loss of heat ; and by tracing backwards the 

 pi'ocess of cooling had formed a definite 

 estimate of the greatest and least number of 

 million years which can possibly have passed 

 since the surface of the earth was every- 

 where red hot. I expressed my conclusion 

 in the following statement : f 



" We are very ignorant as to the effects of high 

 temperatures in altering the conductivities and spe- 

 cific heats and melting temperatures of rocks, and as 

 to their latent heat of fusion. "We must, therefore, 

 allow very wide limits in such an estimate as I have 

 attempted to make ; but I think we may with much 

 probability say that the consolidation cannot have 

 taken place less than 20 million years ago, or we 

 should now have more underground heat than we 

 actually have ; nor more than 400 million years ago, 

 or we should now have less underground heat than 

 we actually have. That is to say, I conclude that 

 Leibnitz's epoch of emergence of the consisieiitior 

 status [the consolidation of the earth from red hot or 

 white hot molten matter] was probably between 

 those dates." 



§17. During the 35 years which have 

 passed since I gave this wide-ranged esti- 

 mate, experimental investigation has sup- 

 plied much of the knowledge then wanting 

 regarding the thermal properties of rocks 

 to form a closer estimate of the time which 

 has passed since the consolidation of the 

 earth, and we have now good reason for 

 judging that it was more than 20 and less 

 than 40 million years ago ; and probably 

 much nearer 20 than 40. 



§ 18. Twelve years ago, in a laboratory 

 established by Mr. Clarence King, in con- 



* ' On the Secular Cooling of the Earth, ' Trans. 

 Roy. Soc. Edinburgh, Vol. XXIII., April 28, 1862, 

 reprinted in Thomson and Tait, Vol. III., pp. 468- 

 485, and Math, and Phys. Papers, art. XCIV., pp. 

 295-311. 



t ' On the Secular Cooling of the Earth,' Math, and 

 Phys. Papers, Vol. III., I 11 of art. XCIV. 



