to Section C [Geology). 455 



Archsean complex, whicli may represent primitive sedimentary 

 rocks, formed under exceptional conditions, and subsequently 

 transformed under the influence of the internal heat of the earth. 

 This, I think, would be Professor Bonney's view. Finally, Lord 

 Kelvin has argued that the life of the sun as a luminous star is even 

 more briefly limited than that of our oceans. In such a case, if our 

 oceans were formed fifty-five millions of years ago, it is possible 

 that after a short existence as almost boiling water they grew 

 colder and colder, till they became covered with thick ice, and 

 moved only in obedience to the tides. The earth, frozen and dark, 

 except for the red glow of her volcanoes, waited the coming of the 

 sun, and it was not till his growing splendour had banished the long 

 night that the cheerful sound of running waters was heard again in 

 our midst. Then the work of denudation and deposition seriously 

 recommenced, not to cease till the life of the sun is spent. Thus 

 the thickness of the stratified series may be a measure rather of the 

 duration of sunlight than of the period which has elapsed since the 

 first formation of the ocean. It may have been so — we cannot tell 

 — but it may be fairly urged that we know less of the origin, 

 histoi'y, and constitution of the sun than of the earth itself, and that, 

 for aught we can say to the contrary, the sun may have been shining 

 on the just-formed ocean as cheerfully as he shines to-day. 



Time required for the Evolution of the Living World. 



But, it will be asked, how far does a period of twenty-six millions 

 satisfy the demands of biology ? Speaking only for myself, although 

 I am aware that eminent biologists are not wanting who share this 

 opinion, I answer, " amply." But it will be exclaimed, " surely 

 there are ' comparisons in things.' " Look at Egypt, where more 

 than 4,000 years since the same species of man and animals lived 

 and flourished as to-day. Examine the frescoes and study the living 

 procession of familiar forms they so faithfully portray, and then tell 

 us, how comes it about that from changes so slow as to be 

 inappreciable in the lapse of forty centuries you propose to build 

 up the whole organic world in the course of a mere twenty-six 

 millions of years ? To all which we might reply that even 

 changeless Egypt presents us with at least one change — the 

 features of the ruling race are to-day not quite the same as those 

 of the Pharaohs. But, putting this on one side, the admitted 

 constancy in some few common forms proves very little, for, so long 

 as the environment remains the same natural selection will conserve 

 the type, and, so far as we are able to judge, conditions in Egypt 

 have remained remarkably constant for a long period. 



Change the conditions, and the resulting modification of the 

 species becomes manifest enough ; and in this connection it is only 

 necessary to recall the remarkable mutations observed and recorded 

 by Professor Weldon in the case of the crabs in Plymouth Harbour. 

 In response to increasing turbidity of the sea-water these crabs have 

 undergone or are undergoing a change in the relative dimensions of 

 the carapace, which is persistent, in one direction, and rapid enough 

 to be determined by measurements made at intervals of a few years. 



