504 



NA 'JUKE 



[Septkmbek 24, 1896 



measure of the rate of deposition of rock ; "for the same 

 material is laid down elsewhere, and would of course add the 

 same height of one foot to some other area equal in size to that 

 from which it was removed. 



The next datum to be obtained is the total thickness of the 

 stratified rocks from the Cambrian system to the present day. 

 "On a reasonable computation these stratified masses, where 

 most fully developed, attain a united thickness of not less than 

 100,000 feet. If they were all laid down at the most rapid 

 recorded rate of denudation, they would require a period of 

 seventy-three millions of years for their completion. If they 

 were laid down at the slowest rate, they would demand a period 

 of not less than 680 millions." 



The argument that geological agencies acted much more 

 vigorously in past times he entirely refuted by pointing to the 

 character of the deposits of which the stratified series is com- 

 posed. "We can see no proof whatever, nor even any evidence 

 which suggests that on the whole the rate cf waste and sedi- 

 mentation was more rapid during Mesozoic and PaUeozoic time 

 than it is to-day. Mad there been any marked difference in 

 this rate from ancient to modern limes, it would be incredible 

 that no clear proof of it should have been recorded in the crust 

 of the earth." 



It may therefore he inferred that the rate of deposition was 

 no nearer the more rapid than the slower of the rales recorded 

 above, and, if so, the stratified rocks would have been laid 

 down in ab<jut 400 million years. 



There are other arguments favouring the uniformity of con- 

 ditions throughout the time during which the stratified rocks 

 were laid down, in addition to those which are purely geological 

 and depend upon the character of the rocks themselves. 

 Although more biological than geological, these arguments are 

 best considered here. 



The geological agency to which attention is chiefly directed 

 by those who desire to hurry up the phenomena of rock forma- 

 tion is that of the tides. But it seems certain that the 

 tides were not sufficiently higher in Silurian times to prevent 

 the deposition of certain beds of great thickness under conditions 

 as tranquil as any of which we have evidence in the case of a 

 formation extending over a large area. From the character of 

 the organic remains it is known that these beds were laid down 

 in the sea, and there are the strongest grounds for believing 

 that they were accumulated along shores and in fairly shallow 

 water. The remains of extremely delicate organisms are found 

 in immense numbers, and over a very large area. The recent 

 discovery, in the Silurian system of America, of trilobites, with 

 their long delicate antenna: perfectly preserved, proves that in 

 one locality (Rome, New York State) the tranquillity of 

 deposition was quite as profound as in any locality yet discovered 

 on this side of the Atlantic. 



There are, then, among the older Palajozoic rocks a set of 

 deposits than which we can imagine none better calculated to 

 test the force of the tides ; and we find that they supply 

 evidence for exceptional tranquillity of conditions over a long 

 period of time. 



There is other evidence of the permanence, throughout the 

 time during which the stratified rocks were deposited, of con- 

 ditions not very dissimilar from those which obtain to-day. 

 Thusthe attachments of marine organisms, which are permanently 

 rooted to the bottom or on the shores, did not differ in strength 

 from those which we now find- an indication that the strains due 

 to the movements of the sea did not greatly differ in the past. 



We have evidence of a somewhat similar kind to prove 

 uniformity in the movements of the air. The expanse of the 

 wings of flying organisms certainly does not differ in a direction 

 which indicates any greater violence in the atmospheric con- 

 ditions. Before the birds had become dominant among the 

 larger flying organisms, their place was taken by the flying 

 reptiles, the pterodactyls, and before the appearance of these 

 we know that, in Pala'ozoic times, the insects were of immense 

 size, a dragon-fly from the Carboniferous rocks of France being 

 upwards of two feet in the expanse of its wings. .\s one group 

 after another of widely dissimilar organisms gained control of the 

 air, each was in turn enabled to increase to the size which was 

 best suited to such an environment, but we find that the limits 

 which obtain to-day were not widely different in the past. .\nd 

 this is evidence for the uniformity in the strains due to wind 

 and storm no less than to those due to gravity. Furthermore, the 

 condition of the earth's surface at present shows us how ex- 

 tremely sensitive the flying organism is to an increase in the 



NO. 1404, VOL. 54 j 



former of these strains, when it occurs in proximity to the .sea. 

 Thus it is well known that an unusually large proportion of 

 the Madeiran beetles are wingless, while tho.se 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 

 individuals 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 cannot live at 

 all in the far more stormy Kerguelen Land, and the whole of 

 the insect fauna is wingless. 



The size and strength of the trunks of fossil trees afford, as 

 Prof. George Darwin has pointed out, evidence of uniformity in 

 the strains due to the condition of the atmosphere. 



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 

 majority of our storms do to-day. 



When, therefore, we are accused of uniformitarianism, as if it 

 were an entirely unproved assumption, we can at any rate point 

 to a large body of positive evidence which supports our con- 

 tention, and the absence of any evidence against it. Further- 

 more, the data on which we rely are likely to increase largely, 

 as the result of future work. 



After this interpolation, chiefly of biological argument in 

 support of the geologist, I cannot do better than bring the 

 geological evidence to a clo.se in the words which conclude Sir 

 Archibald deikie's address : " After careful reflection on the 

 subject, I affirm that the geological record furnishes a mass of 

 evidence which no arguments drawn from other departments ot 

 nature can ex]3lain away, and which, it seems to me, cannot 

 be satisfactorily interpreted save with an allowance of time 

 much beyond the narrow limits which recent phy.sical speculation 

 would concede." 



In his letter to Prof. Perry (Nature, January 3, 1895), Lori.1 

 Kelvin says : — 



" So far as underground heat alone is concerned, you are 

 quite right that my estimate was 100 million, and please remark 

 (P. L. and A., vol. ii. p. 87) 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 considered 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 furthermore that the time must 

 be greatly increased on account of the breaks and interruptions 

 which occur in the series, so that we shall probably get as near 

 an estimate as is 'possible from the data which are available by 

 taking 450 million as the time during which the stratified rocks 

 were formed. 



Before leaving this part of the subject, 1 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 difliculties can be over- 

 come, is certain to lead to results of the greatest interest and 

 importance. Ever since the epoch-making voyage of the 

 C/ialltiixer, it has been known that the floor of the deep oceaiis 

 outside the yellow shelf which fringes the continental areas is 

 covered by a peculiar deposit formed entirely of meteoric and 

 volcanic dust, the waste of floating pumice, and the hard parts 

 of animals living in the ocean. Of these latter only the most 

 resistant can escape the powerful solvent agencies. Many 

 observations prove that the accumulation of ihis deposit is 

 extremely slow. One indication of this is especially convincing : 

 the teeth of sharks and the most resistant pan of the skeleton — 

 the ear-bones— of whales are so thickly spread over the .surface 

 that they are continually brought up in the dredge, while some- 

 times a single haul will yield a large numlier of them. Imagine 

 the countless generations of sharks and whales which must have 

 succeeded each other in order that these insignificant portions 

 of them should be so thickly spread over that vast area which 

 forms the ocean floor. We have no reason to suppose that 

 sharks and whales die more frequently in the deep ocean than 

 in the shallow fringing seas ; in fact, many observations point in 

 the opposite direction, for wounded and dying whales often 

 enter shallow creeks and inlets, and not uncommonly become 

 strandeil. And yet these remains of sharks and whales, although 

 well known in the stratified rocks which were laid down in 



