Sept. 7, 1876] 



NATURE 



403 



zoic have long held their places from the reluctance to disturb 

 established nomenclature, as well as from the difficulty of in- 

 venting appropriate substitutes ; but if retained at all, we know 

 now that the relations they represent are not the same for the 

 terrestrial, the deep oceanic, and the intermediate areas, any 

 more than the life is the same under those three conditions. 



I have ones before called attention to a grave difficulty in the 

 physical geography of Scotland ; and as Mr. Seeley has since 

 then raised the same question without obtaining an answer, 

 I would again state the case as one which seems to involve the 

 revisal of some definitions. 



The Silurian hills of South Scotland are commonly said to 

 have been'covered by Old Red Sandstone and even by Carboni- 

 ferous strata, patches of these rocks being met with on the 

 south side of the fault which defines these hills with their abrupt, 

 coast-like margin seen from Edinburgh, or from Symington sta- 

 tion on the Caledonian line. But the surface of these Silurians 

 was denuded before the Old Red times, as Mr. Geikie has showed. 

 Nay, valleys existed as now, and in the same positions as now. 

 At the present time the rivers flow in identically the same valleys, 

 in at least the cases of the Nith, the Annan, the Lauder, and the 

 Liddell ; and the boundaries of the areas are so well known that 

 we can safely assert no buried channel to exist such as we find 

 on the tributaries of the Clyde. That the channels were occluded 

 in glacial times we may take for certain ; that the obstruction 

 has been washed away and the courses cleared is equally certain. 

 The surface contours were not materially altered, so that the 

 retreating ice lefc hollows in the position of the old valleys. But 

 the case is qui*e differeat when we deal with the older rocks. 

 Their succession is marked by unconformities and overlaps, 

 which it is impossible to picture as associated with full preserva- 

 lion of the surface features on which they were laid down ; and 

 when the thickness comes to be as much as i,oco feet or more, 

 and of that thickness a part at least made up of marine strata, 

 the relapse of all the streams to their old causes is an event of 

 the highest improbability. Mr. Topley has pointed out how the 

 dip of strata may, under certain circumstances, coincide with 

 their thinning out to the margins of their area of deposit, changes 

 of angle in highly inclined strata pointing in the same direction. 

 The ordinary rule of protracting strata, and thus restoring their 

 thickness over the adjacent high ground, is, in the case, at least, 

 of South Scotland, a method which imposes on atmospheric 

 denudation, even if aided by the sea, a most complicated task. 



Had time permitted, it might have been interesting to note 

 the changing phraseology regarding faults, and the pertinacity 

 with which phrases involving the most unsatisfactory and im- 

 probable causation continue to be used. Upcast and down- 

 cast, upthrow and downhrow, displacement upwards or down- 

 wards — these it may be said are of small importance ; they are 

 only symbols. But in the first place they are mischievous so far 

 as they give students confused ideas with which to contend, and 

 in the second place the continued acceptance of loose phraseo- 

 logy is peculiar to geology ; even in metaphysics, where the sub- 

 ject matter is much more conveniently discussed in ordinary lan- 

 guage, new terms are employed to a great extent. Bat important 

 as I therefore regard these terms from the teacher's point of view, 

 the greater importance attaches to the accuracy of the notions 

 which underlie our language regarding the processes and rates of 

 deposit aifd denudation. 



So far as our present knowledge goes, we must accept it as 

 certain that there is some limit to the duration of the earth in the 

 past. Neither philosophers nor astronomers are agreed on the 

 essential points of the problem, nor have they considered all the 

 possible changes in the position of the earth's axis, and in the 

 rate at which the earth loses heat. The limits hitherto prescribed 

 are so discrepant that we cannot as yet accept any as fixed. 

 Neither have geologists so accurate a knowledge of geological 

 processes that they can speak with confidence either of the abso- 

 lute or relative rates at which rock formation has advanced. The 

 geologist has hitherto asked for more time, not because he 

 himself was aware of his need, but from a generous regard for the 

 difficulties in which his zoological brother found himself when he 

 attempted to explain the diversity of the animal series as the 

 result of slowly-operating causes. The geologist asked for more 

 time simply because he could form no just estimate of what was 

 needed for the physical processes with whose results he was 

 familiar. But paloeontological domination is now at an end ; 

 and the increasing number of geologists, who are also competent 

 physicists and mathematicians, seems to mark a new school, 

 which will strive to interpret more precisely the accumulated 

 facts. Such at least seems the history of the past fifteen or I 



twenty years. Such seems the direction in which speculation 

 now tends, and in the foregoing remarks I have endeavoured 

 faithfully to represent the drift of our science. To many here 

 present much of what I have said is already familiar ; I therefore 

 give place to the more legitimate business of the Section, looking 

 to receive elsewhere "such censures as may be my lot." 



SECTION D. 



Biology. 



Opening Address by the President, ALFREt' Russel 

 Wallace. 



Introduction, 



The range of subjects comprehended within this Section is so 

 wide, and my own acquaintance with them so imperfect and 

 fragmentary, that it is not in my power to lay before you any 

 general outline of the recent progress of the biological sciences. 

 Neither do I feel competent to give you a summary of the present 

 status of any one of the great divisions of our science — such as 

 Anatomy, Physiology, Embryology, Histology, Classification, 

 or Evolution— Philology, Ethnology, or Prehistoric Archceo- 

 logy ; but there are fortunately several outlying and more or less 

 neglected subjects to which I have for some time had my atten- 

 tion directed, and which I hope will furnish matter for a few 

 observations, of some interest to biologists, and at the same time 

 not unintelligible to the less scientific members of the Associa- 

 tion who may honour us with their presence. 



The subjects I first propose to consider have no general name, 

 and are not easily grouped under a single descriptive heading ; but 

 they may be compared with that recent development of a sister- 

 science, which 'nas been termed Surface-geology or Earth-sculp- 

 ture. In the older geological works we learnt much about strata, 

 and rocks, and fossils, their superposition, contortions, chemical 

 constitution, and affinities, with some general notions of how 

 they were formed in the remote past ; but we often came to the 

 end of the volume no whit the wiser as to how and why the 

 surface of the earth camcj to be so wonderfully and beautifully 

 diversified ; we were not told why some mountains are rounded 

 and Jothers precipitous ; why some valleys are wide and open, 

 others narrow and rocky; why rivers so often pierce through moun- 

 tain-chains ; why mountain lakes are often so enormously deep ; 

 whence came the gravel, and drift, and erratic blocks, so strangely 

 spread over wide areas while totally absent from other areas 

 equally extensive. So long as these questions were almost 

 ignored, geology could hardly claim to be a complete science, 

 because, while professing to explain how the crust of the earth 

 came to be what it is, it gave no intelligible account of the varied 

 phenomena presented by its surface. But of late years these 

 surface-phenomena have been assiduously studied ; the mar- 

 vellous effects of denudation and glacial action in giving the 

 final touches to the actual contour of the earth's surface, and 

 their relation to climatic changes and the antiquity of man, have 

 been clearly traced, thus investing geology with a new and 

 popular interest, and at the same time elucidating many of the 

 phenomena presented in the older formations. 



Now, just as a surface-geology was required to complete that 

 science, so a surface-biology was wanted to make the science of 

 living things more complete and more generally interesting, by 

 applying the results arrived at by special workers, to the inter- 

 pretation of those external and prominent features whose endless 

 variety and beauty constitute the charm which attracts us to the 

 contemplation or to the study of nature. We have the descrip- 

 tive zoologist, for example, who gives us the external characters 

 of animals ; the anatomist studies their internal structure ; 

 the histologist makes known the nature of their component 

 tissues ; the embryologist patiently watches the progress of their 

 development ; the systematist groups them into classes and orders, 

 families, genera, and species ; while the field-naturalist studies 

 for us their food and habits and general economy. But till quite 

 recently, none of these earnest students, nor all of them combined, 

 could answer satisfactorily, or even attempted to answer, many 

 of the simplest questions concerning the external characters and 

 general relations of animals and plants. Why are flowers so 

 wonderfully varied in form and colour? what causes the Arctic 

 fox and the ptarmigan to turn white in winter ? why are there 

 no elephants in America and no deer in Australia ? why are 

 closely allied species rarely found together ? why are male animals 

 so frequently bright coloured ? why are extinct animals so often 

 larger than those which are now living ? what has led to the 



