216 



ISLAND LIFE. 



[part I. 



present rate of denudation and deposition, is only 28,000,000 

 years. 1 



The Bate of G-eological Change prohaUy greater in very remote 

 times. — The opinion that denudation and deposition went on 

 more rapidly in early times owing to the frequent occurrence of 

 vast convulsions and cataclysms was strenuously opposed by Sir 

 Charles Lyell, who so well showed that causes of the very same 

 nature as those now in action were sufficient to account for all 

 the phenomena presented by the rocks throughout the whole 

 series of geological formations. But while upholding the 

 soundness of the views of the " uniformitarians " as opposed to the 



convulsionists," we must yet admit that there is reason for 

 believing in a gradually increasing intensity of all telluric 

 action as we go back into past time. This subject has been well 

 treated by Mr. W. J. Sollas,^ who shows that, if, as all physicists 

 maintain, the sun gave out perceptibly more heat in past ages 

 than now, this alone would cause an increase in almost all the 

 forces that have brought about geological phenomena. With 

 greater heat there would be a more extensive aqueous atmo- 

 sphere, and a greater difference between equatorial and polar 

 temperatures ; hence more violent winds, heavier rains and snows, 

 and more powerful oceanic currents, all producing more rapid 

 denudation. At the same time, the internal heat of the earth 

 being greater, it would be cooling more rapidly, and thus the 

 forces of contraction — which cause the upheaving of mountains, 

 the eruption of volcanoes, and the subsidence of extensive 

 areas — would be more powerful and w^ould still further aid the 

 process of denudation. Yet again, the earth's rotation was 

 certainly more rapid in very remote times, and this would cause 

 more impetuous tides and still further add to the denuding 



1 From the same data Professor Haughton estimates a minimum of 

 200 million years for the duration of geological time ; but he arrives at 

 this conclusion by supposing the products of denudation to be uniformly 

 spread over the whole sea-hottom instead of over a narrow belt near the 

 coasts, a supposition entirely opposed to all the known facts, and which 

 had been shown by Dr. Croll, five years previously, to be altogether erro- 

 neous. (See Nature, Vol. XVIIL, p. 268, where Professor Haughton's 

 paper is given as read before the Royal Society.) 



^ See Geological Magazine for 1877, p. 1. 



