$20 Geological Society :— 



the lieat of the sun it would be necessary for the sun to have 

 nearly the same proportion of uranium as pitchblende itself. But 

 once. the consistentlor status has been reached, once, that is, solidifi- 

 cation occurs and convective cooling ceases, the formation of the 

 crust and its rapid fall of temperature by radiation enormously 

 reduces the future loss of heat. The geological age is then 

 inaugurated. Then the quantities of radioactive materials found 

 in the earth's crust would maintain the outer layers at sensibly 

 constant temperature throughout the geological nge, while within 

 the heat would gradually accumulate, until inevitably once again 

 the earth must become fluid throughout. "Our geological age 

 inay have been preceded by other ages, every trace of which has 

 perished in the regeneration which has heralded our own." This 

 difficult question of the thermal state of the interior, if perhaps 

 the most important and fascinating, is but one of many to 

 which the new principles of radioactive change are applied. 

 Particular interest attaches to the account of the author's own 

 researches on the rocks of the St. Grothard and Simplon tunnels, 

 and to his conclusion of the importance of the radium content of 

 the rocks in determining the temperature gradient. The views 

 of the author on the part played by the radioactivity in the 

 architecture of mountains, are here extended and elaborated, and 

 in an excellent appendix, the methods employed in the laboratory 

 in estimating the amounts of radium in rocks are explained. 



Illustrative of the great importance and rapid growth of the 

 subject it may be mentioned that already since this book appeared 

 so many important researches have been made that any new 

 edition must be largely a new book. Thorium, here but little 

 referred to, has been shown by the author and others to be of 

 importance geologically almost equal to uranium, while Professor 

 Strutt's most recent researches on the helium in minerals derived 

 from the rocks of various geological horizons bid fair to provide 

 most valuable new data for the evaluation of geological age. It 

 looks indeed as if geology, having been first starved by physics in 

 the matter of time, is now to be given more than it can assimilate. 

 The helium method puts a minimum, estimate on geological age far 

 in excess of any other method of computation. 



LXXXIV. Proceedings of Learned Societies. 



GEOLOGICAL SOCIETY. 

 [Continued from p. 656.] 



December 15th, 1909.— Prof. W. J. Sollas, LL.D., Sc.D., F.R.S., 

 President, in the Chair. 



npplE following communications were read : — 



1. ' The Skiddaw Granite and its Metamorphism.' By Hubert 

 Heron Rastall, M.A., F.G.S. 



The visible exposures of the Skiddaw Granite are three in number, 

 all very similar ; part of the more northerly one is a grcisen, which 



