Skptember 24, 1896J 



NA TURE 



497 



studied in great detail.' I shall presently have more to say 

 with regard to work connected with the lithological characters 

 of the sediments. Whilst mentioning glacial denudation, let 

 me allude to a piece of work \\ hich should be done in great 

 detail, though it is not, strictly speaking, connected with 

 stratigraphy, namely, the mapping of the rocks around asserted 

 " rock-basins.' I can find no actual proof of the occurrence of 

 such basins in Britain, and it is very desirable that the solid 

 rocks and the drift should be carefully inserted on large-scale 

 maps, not only all around the shores of several lakes, but also 

 between the lakes and the sea, in order to ascertain whether 

 the lakes are really held in rock-basins. Until this work is 

 done, however probable the occurrence of rock-basins in Britain 

 may be considered to be, their actual existence cannot be 

 expected to be proved. 



When referring to the subject of denudation, mention was 

 made a moment ago of the study of the lithological character of 

 the sediments. Admirable work in this direction was carried 

 out years ago by one who may be said to have largely changed 

 the direction of advance of geology in this country owing to his 

 researches " On the Microscopical Structure of Crystals, indicat- 

 ing the Origin of Minerals and Rocks." I refer, of course, to 

 Dr. 11. C. Sorby. But since our attention has been so largely 

 directed to petrolog)', the study of the igneous and metamorphic 

 rocks has been most zealously pursued, whilst that of the sedi- 

 ments has been singularly little heeded, with few exceptions, 

 prominent amongst which is the work of Mr. Maynard Ilutch- 

 ings, the results of which have been recently published in the 

 Geological Magazine, though we must all hope that the details 

 which have hitherto been supplied to us, valuable as they are, 

 are only a foretaste of what is to follow from the pen of this able 

 observer. Descriptions of the lithological changes which occur 

 in a vertical series of sediments, as well as of those which are 

 observed when any particular band is traced laterally, will no 

 doubt throw light upon a number of interesting questions. 



Careful work amongst the ancient sediments, especially those 

 which are of organic origin, has strikingly illustrated the general 

 identity of characters, and therefore of methods of formation, of 

 deposits laid down on the sea-floors of past times and those which 

 are at present in course of construction. Globigerine-oozeshave 

 been detected at various horizons and in many countries. Prof. 

 H. Alleyne Nicholson (Nicholson and Lydekker, " Manual of 

 Pala;onlology," chap, ii.) has described a pteropod-ooze of 

 Devonian age in the Hamilton Limestone of Canada, which is 

 largely composed of the tests olStyliola : and to Dr. G.J. Hinde 

 we owe the discovery of a large number of radiolarian cherts of 

 Palarozoic and Neozoic ages in various parts of the globe. The 

 extreme thinness of many argillaceous deposits, which are re- 

 presented elsewhere by hundreds of feet of strata, suggests that 

 .some of them, at any rate, may be analogous to the deep-sea 

 clays of modern oceans, though in the case of deposits of this 

 nature we must depend to a large extent upon negative evidence. 

 The uniformity of character of thin marine deposits over wide 

 areas is in itself evidence of their formation at some distance 

 from the land ; but although the proofs of origin of ancient 

 sediments far from coast-lines may be looked upon as per- 

 manently established, the evidence for their deposition at great 

 depths below the ocean's surface might be advantageously 

 increased in the case of many of them. The fairly modern sedi- 

 ments, containing genera which are still in existence, are more 

 likely to furnish satisfactory proofs of a deep-sea origin than are 

 more ancient deposits. Thus the existence of Arc/iirnpiiemfes 

 and Cyslechiiius in the oceanic series of Barbadoes, as described 

 by Dr. Gregory, furnishes strong proofs of the deep-sea 

 character of the deposits, whilst the only actual argument in 

 favour of the deep-.sea character of certain Pali^ozoic sediments 

 has been put forward by Prof Suess, who notes the similarity 

 of certain structures of creatures in ancient rocks to those 

 possessed by modern deep-sea Crustacea, especially the co-exist- 

 ence of trilobites which are blind with those which have 

 enormously developed eyes. 



A question which has been very prominently brought to the 

 fore in recent years is that of the mode of formation of certain 

 coral-reefs. The theory of Charles Darwin, lately so widely 

 accepted as an explanation of the mode of formation of barrier- 

 reefs and atolls, has been, as is well known, criticised by Dr. 



* It is desirable that the boulders of sediment.iry rock imbedded in the 

 drifts of East Anglla sliould be carefully_ examined and fossils collected 

 from ihcm. The calcareous strata .xssocialed with the Alum .Shales of 

 Scandinavia and the strata of the Orthoceras-Limestone of that region may 

 be expected to be represented amongst the boulders. 



NO. 1404, VOL. 54] 



Murray, with the result that a large number of valuable observ- 

 ations have been recently made on modern reefs, especially by 

 biologists, as a contribution to the study of reef formation. Nor 

 have geologists been inactive. Dr. E. Mojsisovics and Prof. 

 Dupont, to mention two prominent observers, have described 

 knoll-like masses of limestone more or less analogous, as regards- 

 structure, to modern coral-reefs. They consider that these have 

 been formed by corals, and indeed Dupont maintains that the 

 atoll-shape is still recognisable in ancient Devonian coral-reefs 

 in Belgium.' I would observe that all cases of " knoll-reefs ''' 

 of this character have been described in districts which furnish 

 proofs of having been subjected to considerable orogenic dis- 

 turbance, subsequent to the formation of the rocks composing 

 the knoll-shaped masses, whilst in areas which have not been 

 affected by violent earth-foldings, the reef-building corals, so far 

 as 1 have been able to ascertain, give rise to sheet-like masses, 

 such as should be produced according to Dr. Murray's theory. 

 I would mention especially the reefs of the Corallian Rocks of 

 England, and also some admirable examples seen amongst the 

 Carboniferous Limestone strata of the great western escarpment) 

 of the Pennine chain which faces the Eden valley in the neigh- 

 bourhood of Melmerby in Cumberland. Considering the number 

 of dissected coral-reefs which exist amongst the strata of the 

 earth's crust, and the striking way in which their structure is- 

 often displayed, it is rather remarkable that comparatively little 

 attention has been paid to them by geologists in general, when 

 the subject has been so prominently brought before the scientific 

 world, for we must surely admit that we are much more likely 

 to gain important information, shedding light upon the methods- 

 of reef-formation, by a study of such dissected reefs, than by 

 making a few bore-holes on some special coral island. I would 

 specially recommend geologists to make a detailed study of the 

 British coral-reefs of Silurian, Devonian, Carboniferous, and 

 Jurassic ages. 



Turning now to organic deposits of vegetable origin, we must, 

 as the result of detailed work, be prepared to admit the in- 

 applicability of any one theory of the formation of coal seams. 

 The " growth-in-place" theory inay be considered fairly well 

 established for some coals, such as the spore-coals, whilst the 

 " drift " theory furnishes an equally satisfactory explanation of 

 the formation of cannel-coal. It is now clear that the applica- 

 tion of the general term coal io a number of materials of diverse 

 nature, and probably of diverse origin, was largely responsible 

 for the dragging-out of a controversy, in which the champions of 

 either side endeavoured to explain the origin of all coal in one 

 particular way. 



The stratigraphical geologist, attempting to restore the physical 

 geography of former periods, naturally pays much attention to 

 the positions of ancient coast-lines; indeed, all teachers find it 

 impossible to give an intelligible account of the stratified rocks- 

 without some reference to the distribution of land and sea at 

 the time of their formation. The general position of land-mas.se^ 

 at various times has been ascertained in several parts of the 

 world, but much more information must be gathered together 

 before our restorations of ancient sea-margins approximate to- 

 the truth. The carboniferous rocks of Britain have been specially 

 studied with reference to the distribution of land and water 

 during the period of their accumulation, and yet we find that 

 owing to the erroneous identification of certain rocks of Devon- 

 shire as grits or sandstones, which Dr. Hinde has shown to be 

 radiolarian cherts, land was supposed to lie at no great distance 

 south of this region in Lower Carboniferous times, whereas the 

 probabilities are in favour of the existence of an open ocean at 

 a consideral)le distance from any land in that direction. This- 

 case furnishes us with an excellent warning against generalisatioit 

 upon insufficient data. 



As a result of detailed study of the strata, the effects of earth- 

 movements have been largely made known to us, especially of 

 those comparatively local disturbances spoken of as orogenic 

 which are mainly connected with mountain-building, whilst 

 information concerning the more widely spread epeirogenic 

 movements is also furnished by a study of the stratified rocks. 

 The structure of the Alps, of the North-West Highlands of 

 Scotland, and of the uplifted tracts of North America is now 

 familiar to geologists, whilst the study of comparatively recent 

 sediments has proved the existence of widespread and extensive 

 movements in limes which are geologically modern ; for instance, 



1 .Similar knoll-like masses have been described in this country by Mr. 

 R. H. Tiddeman, as occurring in the Craven district of Yorkshire, but he 

 does not attribute their formation to coral growth to any great extent. 



