October 30, 1896.] 



SCIENCE. 



635 



it occurs in proximity to the sea. Thus it 

 is well known that an unusually large pro- 

 portion of the Madeiran beetles are wing- 

 less, while those which require the power 

 of flight possess it in a stronger degree than 

 on continental areas. This evolution in 

 two directions is readily explained by the 

 destruction, by drowning, of the winged in- 

 dividuals of the species which can manage 

 to live without the power of flight, and of the 

 less strongly winged individuals of those 

 which need it. Species of the latter kind 

 <3annot live at all in the far more stormy 

 Kerguelen Land, and the whole of the in- 

 sect fauna is wingless. 



The size and strength of the trunks of 

 fossil trees afibrd, as Prof. George Darwin 

 lias pointed out, evidence of uniformity in 

 the strains due to the condition of the at- 

 mosphere. 



We can trace the prints of raindrops at 

 various geological horizons, and in some 

 cases found in this country it is even said 

 that the eastern side of the depressions is 

 the more deeply pitted, proving that the 

 rain drove from the west, as the great ma- 

 jority of our storms do to-day. 



When, therefore, we are accused of uni- 

 formitarianism, as if it were an entirely un- 

 proved assumption, we can at any rate point 

 to a large body of positive evidence which 

 supports our contention, and the absence of 

 any evidence against it. Furthermore, the 

 data on which we rely are likely to increase 

 largely, as the result of future work. 



After this interpolation, chiefly of biologi- 

 cal argument in support of the geologist, I 

 cannot do better than bring the geological 

 evidence to a close in the words which con- 

 clude Sir Archibald Geikie's address : " After 

 careful reflection on the subject, I aflirm 

 that the geological record furnishes a mass 

 of evidence which no arguments drawn from 

 other departments of Nature can explain 

 away, and which, it seems to me, cannot be 

 satisfactorily interpreted save with an al- 



lowance of time much beyond the narrow 

 limits which recent physical speculation 

 would concede." 



In his letter to Prof. Perry,* Lord Kelvin 

 says : "So far as underground heat alone is 

 concerned, you are quite right that my es- 

 timate was 100 million, and please remark f 

 that that is all Geikie wants; but I should 

 be exceedingly frightened to meet him now 

 with only 20 million in my mouth." 



We have seen, however, that Geikie con- 

 sidered the rate of sedimentation to be, on 

 the whole, uniform with that which now 

 obtains, and this would demand a period of 

 nearly 400 million years. He points out, fur- 

 thermore, that the time must be greatly in- 

 creased on account of the breaks and inter- 

 ruptions which occur in the series, so that 

 we shall probably get as near an estimate 

 as is possible from the data which are avail- 

 able by taking 450 million as the time dur- 

 ing which the stratified rocks were formed. 

 Before leaving this part of the subject, I 

 cannot refrain from suggesting a line of 

 enquiry which may very possibly furnish 

 important data for checking the estimates 

 at present formed by geologists, and which, 

 if the mechanical difiiculties can be over- 

 come, is certain to lead to results of the 

 greatest interest and importance. Ever 

 since the epoch-making voyage of the ' Chal- 

 lenger ' it has been known that the floor 

 of the deep oceans outside the shallow shelf 

 which fringes the continental areas is cov- 

 ered by a peculiar deposit formed entirely 

 of meteoric and volcanic dust, the waste of 

 floating pumice and the hard parts of ani- 

 mals living in the ocean. Of these latter 

 only the most resistant can escape the 

 powerful solvent agencies. Many observa- 

 tions prove that the accumulation of this 

 deposit is extremely slow. One indication 

 of this is especially convincing ; the teeth 

 of sharks and the most resistant part of the 



* Nature, January 3, 1895. 

 tP. L. and A., Yo\. II., p. 87. 



