400 



NATURE 



[Sepi. 7, 1876 



attention. In venturing criticism of this kind, I am not un- 

 mindful of the Nemesis which has overtaken my colleague, Sir 

 W. Thomson, for his comments on Lyell's language. Thomson 

 took exception to language wrhich implied a kind of perpetual 

 motion — a circulation of energy at variance with the teaching of 

 physics ; and behold, two or three years after, Lockyer has 

 published, as a physical astronomer, and Prestvvich has approved, 

 as a geologist, the opinion that the temperature of the sun may 

 have fluctuated — that, in fact, changes of chemical combination 

 may from time to time have refreshed the heat of the planet, 

 whose uniform rate of cooling Sir William had assumed. 



When stratigraphical geology first received due attention, the 

 notion was prevalent that each formation terminated suddenly by 

 cataclysm ; it was therefore natural that the British succession — 

 the earliest to be tabulated in detail— should be taken as a 

 standard for other countries, and that the enumeration of the 

 series should be a generalised section in which were incor- 

 porated those strata not present in Britain. The "intercalation" 

 of beds thus practised to make an "incomplete" series "com- 

 plete " still survives, as do the terms, though the notions which 

 underlie them are formally denied by those who use them. A 

 patriotic fellow-countryman once surprised us by his vehement 

 denunciation of a treacherous Scot who called the Lanarkshire 

 limestones meagre and incomplete as compared with the English. 

 With knowledge he might have made his criticism useful ; as it 

 was he only gave a' fresh example of the national peculiarity 

 which, if it cannot prove Scotland to be better off than its 

 neighbours, is content to make it out to be no worse. The 

 abundant fossils of the Mesozoic strata of England and France 

 rendered comparison easy, and created the impression that con- 

 chology was the A B C of geology, physical being subordinated 

 to palseontological evidence. The balance has been somewhat 

 restored by the Geological Survey, the precision of whose physical 

 observations enables them to guide the paleontologist as often as 

 guided by him. But one legacy from our predecessors we have 

 not got rid of, nor indeed has its value been much called in 

 question. 



The process of intercalation had at first to do only with 

 observed gaps into which obvious equivalents could be received. 

 But as the needs of speculative biology rapidly increased, in the 

 same ratio did belief in the imperfection of the geological record 

 increase, till now we have that record described as a most frag- 

 mentary volume, nay as the remains of the last volume whose 

 predecessors are lost to us. 



Sir W. Thomson did good service by calling in question, on 

 physical grounds, the indefinite extension backwards of geological 

 time. The first fruits of his crusade were the definitions of Uni- 

 form itarianism and Evolution which Prof. Huxley gave. Hence- 

 forth no one will maintain the onesided notions regarding these 

 two opposing views of the earth's history which were adopted in 

 ignorant misconception or dictated by conceit and bigotry. But 

 the service done was even greater, for while it became clear that 

 a knowledge of physics was indispensable to him who would 

 promulgate sound notions, it was further apparent tha.t both 

 biological and geological evolution had a limit in time ; that in 

 fact, on the assumption of the primitive incandescence of our 

 globe, the date might be at least approximately fixed when the 

 mechanical processes now at work commenced, and when the 

 surface of the earth became habitable. Nothing more has yet 

 been done than to point out the way ; for, though Prof. Guthrie 

 Tait indicates a limit of from fifteen to ten millions of years, 

 that statement can only be regarded as in effect, though not 

 perhaps in intention, as a protest against the liberality and vague- 

 ness of Sir W. Thomson's allowance, which gave geologists a 

 range of one to two hundred millions of years. 



Ihe reconciliation of physicists and geologists is not likely 

 to come through Mr. Lockyer's researches, even if the 

 earth's history be shown to have been identical, unless the 

 renewal of the earth's heat be shown to be compatible with con- 

 tinued life on the surface. If the reconciliation is looked for 

 through the prolonged duration of the sun's life, that being the 

 gauge of the earth's duration, the expectation is still based on 

 the supposed need of very great time for geological processes, or 

 rather on the supposed need of very great time for biological 

 evolution, to which geological evolution has been squared. 

 There is another direction in which these results may help us to 

 meet the limitation assigned by the physicists ; the intervals of 

 variation of temperature may be shorter than those which 

 separate the maxima of eccentricity of the earth's orbit, and thus 

 the repeated cold periods of which we have suggestions in the 



stratified rocks, may have recurred within a shorter total period 

 than is at present claimed. 



It is scarcely within the compass of this address to enter into 

 the questions involved, but it is permissible to indicate the 

 reason for delaying meanwhile acceptance of any precise limit of 

 time. There is as yet too much diversity of opinion as to the 

 elements of the problem. Physicists are by no means at one as 

 to the conditions which permit or prohibit shifting of the earth's 

 axis. Calculations are based on the assumption of the regularity 

 of the earth's form under a certain constant relation of the masses, 

 albeit of diverse specific gravity, which compose it. It is more- 

 over assumed that the ratio of land and water has been uniform, 

 though the formation of the grand features of the land by con- 

 traction of the cooling mass has not yet been considered as affect- 

 ing this assumption by altering the disposition of the water. On 

 the one hand it has been shown that the existence of uniform 

 temperatures over the earth's surface is a gratuitous hypothesis ; 

 on the other hand it is clear that the existing distribution of light 

 and heat is incompatible with the flourishing of an abundant 

 Carboniferous and Miocene flora within a short distance of the 

 North Pole. One expects that astronomers will look to the 

 shifting of the axis of rotation as the possible explanation of the 

 difficulty, taking into account likewise the shifting of the centre 

 of gravity necessarily following those displacements of matter 

 which, on the contraction theory, have determined the positions 

 of the main continents and oceans. 



Mr. Evans, in his address to the Geological Society, referred 

 to the deviation of the magnetic axis as perhaps due to such 

 shifting of the materials composing the inner mass of our globe. 

 .May not the conjectures of M. Elie de Beaumont be after all in 

 the right direction ? May not the change of trend which led him 

 to classify the mountain-chains by reference to the age at which 

 they had been elevated, be associated with movements which did 

 not in all cases result in shiftings of the earth's axis, so pro- 

 nounced as those which permitted the Carboniferous and Miocene 

 floras to invade successfully the Arctic Regions, or the pheno- 

 mena of the glacial epoch or epochs, to manifest themselves in 

 the low latitudes when their traces have been recognized ? 



Waiving, for the present, inquiry into the influence which 

 the admission of a possible shifting of the earth's axis might have 

 on our estimate of geological time, I shall return to the phrase- 

 ology whose amendment seems advisable. 



The confusion which exists is well illustrated in a remark by 

 an eminent writer to the effect that the progress of geological 

 research tends to prove the "continuity of geological time." 

 The phrase in itsen involves an absurdity ; but what is meant is, 

 that the successive so-called formations pass into each other by 

 imperceptible gradation ; and that, as time goes on, we sbaU be 

 more and more able to intercalate strata so as to present a con- 

 tinuous scale of animal and vegetable forms. This is one out of 

 many samples of the extreme length to which the thirst for strict 

 correlation may go. We find in Murchison's writings and else- 

 where pointed protests against the succession of strata in one 

 district being held to rule that in other districts ; but these are 

 rather concessions wrung from their author by the pressure of 

 particular instances than acknowledgments of a rule applicable 

 to contiguous and to distinct localities alike. I could not per- 

 haps take a better example than the strata which contain the 

 remains of the fossil Eqtiidce. If we arrange the fossils in any 

 series representing the modification of particular structures, or 

 averaging the modifications of all the structures, we shall find 

 that the terms of the series are met with, now in Europe, now in 

 America ; yet no one would venture to intercalate the European 

 in the American Tertiary series so as to square the geological 

 record with an assumed zoolo.ical standard. The notion of 

 gradations, the extreme view of correlations has led to results 

 which are, to put it mildly, of doubtful value. Yet it was a 

 natural result of the work of Cuvier and other paleontologists 

 among the Mesozoic and Eocene fossiliferous deposits. The 

 statistical method invented by Lyell is simply a mode of grada- 

 tions. Intercalation of strata is therefore a survival from an 

 earlier stage of the science, and carries with it a distinct echo of 

 the catastrophic notion that strata were formed simultaneously 

 and generally over the earth's surface, if not universally. 



The geological record has been compared to a volume of which 

 pages have here and there disappeared ; and the iucompletene.-s 

 of the record has been inferred from the frequency of pronounced 

 gaps in the succession of strata. Of these gaps, these unconfor- 

 mities, Prof. Ramsay has shown the importance by demonstrat- 

 ing that they represent the lapse of unknown, but varying, and 



