734 EEPORT— 1893. 



Lyell ; but of late tliere has been a tendency to bark back to a modified form of 

 Wernerism. This tendency can, I think, be largely traced to the recognition of 

 evolution as a factor in biology and physical astronomy. The discoveries in these 

 sciences may necessitate a modification of the views held by some of the extreme 

 advocates of uniformitarianism. This admission, hovcever, by no means carries 

 with it the conclusion that the methods based on the doctrine of uniformitarianism 

 must be discarded. If I read the history of geology aright, every important 

 advance in the theoretical interpretation of observed facts relating to physical 

 geology has been made by the application of these methods. It does not, of course, 

 foUow that the progress in the future will be exactly along the same lines as that 

 in the past ; but, if I am right in the opinion I have expressed, it is a strong reason 

 for adhering to the old methods until they have been proved to be inapplicable to 

 at least some of the facts with which the physical geologist has to deal. Let us 

 consider for a moment whether the recognition of evolution as a factor in biology 

 and physical astronomy gives an a priori probability to some form of Wernerism. 



The period of time represented by our fossiliferous records is perhaps equivalent 

 to that occupied by the evolution of the vertebrata, but all the great subdivisions 

 of the invertebrata were living in the Cambrian period, and must have been 

 differentiated in still earlier times. Is it not probable, therefore, that the fossili- 

 ferous records at present known represent a period insignificant in comparison 

 with that during which life has existed upon the earth ? Again, is it not probable 

 that the period during which life has existed is a still smaller fraction of that 

 which has elapsed since the formation of the primitive crust ? And if so, what d 

 priori reason have we for believing that the rocks accessible to observation contain 

 the records of the early stages of the planet's history ? But the advocates of the 

 diluted forms of Wernerism which find expression in geological writings at the 

 present day almost invariably refer to recent speculations in cosmical physics. The 

 views of astronomers have always had a powerful influence on those of geologists. 

 Hutton wrote at a time when the astronomical world had been profoimdly affected 

 by Lagrange's discovery, in 1776, of the periodicity of the secular changes in the 

 forms of the planetary orbits. The doubts as to the stability of the solar system 

 which the recognition of these changes had inspired were thus removed, and astro- 

 nomers could then see in the physical system of the universe ' no vestige of a 

 beginning — no prospect of an end." Now it is otherwise. Tidal friction and the 

 dissipation of energy by the earth and by the sun are each referred to as fixing a 

 limit to the existing conditions. I have not the knowledge necessary to enable me 

 to discuss these questions, and I will therefore admit, for the sake of argument, 

 that the phenomena referred to indicate the lines along which the physical evolu- 

 tion of our planet has taken place ; but does it follow that geologists should desert 

 a working hypothesis which has led to brilliant results in the past for one which 

 has been tried again and again and always found wantinsr ? 



If there were absolute unanimity amongst mathematical physicists, it might be 

 necessary for us to reconsider our position. This, however, is not the case. After 

 referring to the argument from tidal friction, Professor Darwin, in his address to 

 the Mathematical and Physical Section for 1886, says: — 'On the whole, then, I 

 can neither feel the cogency of the argument from tidal friction itself, nor, accepts 

 ing it, can I place any reliance on the limits which it assigns to geological history.' 

 In reviewing the argument from the secular cooling of the earth, he points out 

 that the possibility of the generation of heat in the interior by tidal friction has 

 been ignored, and that the thermal data on which the calculations are based are 

 not sufficiently complete to remove all reasonable doubt. lie regards the case 

 depending on the secular cooling of the sun as the strongest ; but it is evident 

 that, in view of undreamt-of possibilities, he would not allow it to have much 

 weight in the face of adverse geological evidence. In conclusion he says : — 

 ' Although speculations as to the future course of science are usually of little avail, 

 yet it seems as likely that meteorology and geology will pass the word of command 

 to cosmical physics as the converse. At present our knowledge of a definite limit to 

 geological time has so little precision that we should do wrong to summarily reject 

 any theories which appear to demand longer periods of time than those which now 



