74 



NA TURE 



\_Mav 25, 1882 



America ; while a third, on the geology of the Falkland 

 Islands, was published later. 



While dealing with the subterranean agents in geolo- 

 logical charge, he kept at the same time an ever watchful 

 eye upon the superficial operations by which the surface 

 of the globe is modified. He is one of the earliest writers 

 jnise the magnitude of the denudation to which 

 even recent geological accumulations have been sub- 

 jected. One of the most impressive lessons to be learnt 

 from his account of Volcanic Islands is the prodigious 

 extent to which they have been denuded. As just stated 

 he was disposed to attribute more of this work to the 

 action of the sea than most geologists would now admit ; 

 but he lived himself to modify his original views, and on 

 this subject his latest utterances are quite abreast of the 

 time. It is interesting to note that one of his early geo- 

 logical papers was on the Formation of Mould (1840), and 

 that after the lapse of forty years he returned to this sub- 

 ject, devoting to it the last of his volumes. In the first 

 sketch we see the patient observation and shrewdness of 

 inference so eminently characteristic of the writer, and in 

 the finished work (so recently noticed in these columns) 

 the same faculties enriched with the experience of a long 

 and busy life. In bringing to light the operations of the 

 earthworm, he called the attention of geologists to an 

 agency, the real efficiency of which they probably do not 

 yet appreciate. Elie de Beaumont looked upon the layer 

 of grass-covered soil as a permanent datum-line from 

 which the denudation of exposed surfaces might be mea- 

 sured. But, as Darwin showed, the constant transference 

 of soil from beneath to the surface, and the consequent 

 exposure of the materials so transferred to be dried and 

 blown away by wind, or to be washed to lower levels by 

 rain, must tend slowly but certainly to lower the level 

 even of undisturbed grass-covered land. 



To another of his early papers reference may be made 

 from its interest in the history of British geology. Buck- 

 land, following in the footsteps of Agassiz, had initiated 

 that prodigious amount of literature which has now been 

 devoted to the records of the Glacial period in this 

 country, by reading to the Geological Society a paper 

 " On Diluvio-glacial Phenomena in Snowdonia and in 

 Adjacent Parts of North Wales" (1841). Darwin, 

 whose wanderings in South America had led him to 

 reflect deeply upon the problems presented by erratic 

 blocks, took an early opportunity of visiting the Welsh 

 district described by Buckland, and at once declared 

 himself to be a believer in the former presence of glaciers 

 in Britain. His paper (1843) in which this belief is stated 

 and enforced by additional observations, stands almost at 

 the top of the long list of English contributions to the 

 history of the Ice Age. 



The influence exercised upon the progress of geology 

 by Darwin's researches in other than geological fields, is 

 less easy to be appraised. Yet it has been far more wide- 

 spread and profound than that of his direct geological 

 work. Even as far back as the time of the voyage of the 

 lie had been led to reflect deeply on some of 

 Lyell's speculations upon the influence of gi 

 changes on the geographical distribution of animals. 

 From that time the intimate connection between geo- 

 istory and biological progress seems to have been 

 continually present in his mind. It was not, however, 



until the appearance of the " Origin of Species" in 1859 

 that the full import of his reflections was perceived. His 

 chapter on the "Imperfection of the Geological Record" 

 startled geologists as from a profound slumber. It would 

 be incorrect to say that he was the first to recognise the 

 incompleteness of the record ; but certainly until the 

 appearance of that famous chapter the general body of 

 geologists was blissfully unconscious of how incredibly 

 fragmentary the geological record really is. Darwin 

 showed why this must necessarily be the case ; how 

 multitudes of organic types, both of the sea and of the 

 land, must have decayed and never have been preserved 

 in any geological deposit ; how, even if entombed in such 

 accumulations, they would in great measure be dissolved 

 away by the subsequent percolation of water. Return- 

 ing to some of his early speculations he pointed out that 

 massive geological deposits rich in fossils, could only 

 have been laid down during subsidence, and only where 

 the supply of sediment was sufficient to let the sea re- 

 main shallow, and to entomb the organic remains on 

 its floor before they had decayed. Hence, by the very 

 conditions of its formation, the geological record, in- 

 stead of being a continuous and tolerably complete 

 chronicle, must almost necessarily be intermittent and 

 fragmentary. The sudden appearance of whole groups 

 of allied species of fossils on certain horizons had 

 been assumed by some eminent authorities as a fatal 

 objection to any doctrine of the transmutation of 

 species. But Darwin now claimed this fact as only 

 another evidence of the enormous gaps in geological 

 history. Reiterating again and again that only a small 

 fraction of the world had been examined geologically and 

 that even that fraction was still but imperfectly known, he 

 called attention to the history of geological discovery as 

 furnishing itself a strong argument against those who 

 argued as if the geological record were a full chronicle of 

 the history of life upon the earth. There is a natural 

 tendency to look upon the horizon upon which a fossil 

 species first appears as marking its birth, and that on which 

 it finally disappears as indicating its extinction. Darwin 

 declared this assumption to be "rash in the extreme.'' 

 No palaeontologist nor geologist will now gainsay this 

 assertion. And yet how continually do we still hear men 

 talking of the stages of the geological record, as if these 

 were sharply marked off everywhere by the first appear- 

 ance and final disappearance of certain species. The bold- 

 ness with which Darwin challenged some of these long- 

 rooted beliefs is not less conspicuous than the modesty 

 and deference with which his own suggestions were always 

 given. " It is notorious," he remarked, " on what exces- 

 sively slight differences many palaeontologists have 

 founded their species ; and they do this the more readily 

 if the specimens come from different sub-stages of the 

 same formation." 



Starting from this conception of the nature of the 

 geological record, Darwin could show that the leading 

 facts made known by palaeontology could be explained by 

 his theory of descent with modification through natural 

 selection. New species had slowly come in, as old ones 

 had slowly died out. Once the thread of succession had 

 been broken it was never taken up again an extinct 

 species or group never reappeared, yet extinction was a 

 slow and unequal process, and a few descendants of 



