March i, 1888] 



NATURE 



425 



of the organisms by which they were formed. But, even in the 

 case of many arenaceous and argillaceous deposits, living organ- 

 isms have played a very important part in their formation. 

 Much of the materials of such rocks can be shown to have been 

 used in building the coverings of organisms, to have filled up 

 their dead shells, or to have been passed through their bodies, 

 before being finally buried under other masses Rocks destitute 

 oi all traces of the solid parts of animals oil .n abound with 

 worm-tracks, burrows, or casts. 



The study of the processes by which similar rock masses are 

 being formed at the present day constitutes the only safe guide 

 to us in interpreting the structures presented by ancient rock- 

 masses. Geologists look forward with much interest to the 

 publication of those volumes of the CJiaUengcr Reports, in which 

 Mr. Murray and M. Renard will deal with these important 

 questions. 



We may especially call attention to two classes of errors that 

 have had much to do with the false conclusions which have been 

 arrived at concerning the conditions under which various deposits 

 have been formed in past geological times. 



In the first place, it has been tacitly assumed that all marine 

 organisms which come from regions bordering the equator must 

 necessarily have lived under tropical conditions. It would be 

 quite as reasonable to treat the mosses and dwarf willows which 

 border the eternal snows of Chimborazo and Kilima-Njaro as 

 tropical plants. Just as mountains rising in equatorial lands to 

 the limit of perpetual snow exhibit on their slopes every gradation 

 of climate from tropical to frigid, so the depths of the oceans, as 

 we now know, exhibit a perfectly similar transition. As we go 

 downwards not only heat, but light also, rapidly diminishes, and 

 many forms which, because they came from equatorial regions, 

 we have hitherto regarded as tropical, we now know to live in 

 icy-cold water as well as in almost utter darkness. 



The large size and abundant development of Cephalopods, 

 Crustaceans, and fish we now know, from recent deep-sea re- 

 searches, to be no evidence whatever of the presence either of 

 warmth or of light ; and Sir Joseph Hooker has abundantly 

 shown the fallacy of similar reasoning when applied to plant-life. 

 I feel sure that, when the full consequences of these important 

 considerations come to be appreciated, the apparent anomalies of 

 many of the supposed climatal conditions of past geological 

 times will altogether disappear. For my own part, I have never 

 felt any difficulty in accepting, as fully equal to the explanation 

 of the facts of the case, the Lyellian doctrine of climate being 

 determined by great changes in the relative positions of the 

 land and water of the globe. 



The other cause of misconception with respect to the conditions 

 which must have prevailed during the deposition of geological 

 deposits consists in the acceptance of an utterly false pro- 

 position, which, though seldom formulated, is often tacitly acted 

 U[)on ; namely, " If two organisms exhibit similarity of structure, 

 their environment i^iust have been the same." 



There never has been wanting abundant evidence of the fallacy 

 of this doctrine. The general structure of the piscivorous bear 

 of the Arctic regions, and of the frugivorous bear of the Malay 

 peninsula, the ostejlogy of the deer of Lapland and of India 

 respectively, exhibit no such differences as would lead us to infer 

 th?ir diversity of habits and surroundings. It has long been 

 known that elephants, rhinoceroses, and hippopotami, with lions, 

 tigers, and hycenas, flourished under Arctic conditions. The 

 deep-sea researches have so added to our knowledge concerning 

 the conditions under which different forms of life exist — 

 especially those belonging to marine faunas — as to demand a 

 complete reconsideration of the conclusions usually accepted by 

 geologists. For there is a general consensus of opinion among 

 the naturalists who have studied the different gr.ups of the deep- 

 sea faunas, that, contrary to what might have been anticipated 

 from the very remarkable conditions under which they live, the 

 deep-sea form-; belong, for the most part, to the same families, 

 and often indeed to the same genera, as shallow-water forms. 



The bearing of this important conclusion upon the great 

 problem of the distribution of marine forms of life is obvious. 

 Botanists have naturally availed themselves of the proved occur- 

 rences of colder climates in many areas to explain difficult facts 

 of plant-distribution, such as the occurrence of well-known Arctic 

 species on the tops of mountains in what are now temperate, or 

 even tropical, districts. But zoologists, now that they know it 

 to be possible for littoral forms to stray into abysmal portions of 

 the ocean, and then subsequently, without profound modifica- 

 tion, to re-emerge in other littoral areas, may find a clue to some 



very remarkable facts concerning the distribution ! of marine 

 forms of life, without having to resort to explanations which 

 seem necessaiy in the case of the terrestrial forms of life which 

 appear to be more dependent than the marine types on the 

 circumstances of their environment. 



The whole problem of the distribution of marine forms of life 

 requires indeed to be worked out afresh on the basis of these new 

 discoveries ; and when this is done, the first to profit by the new 

 generalizations will be geologists, who have long been eon- 

 fronted by seemingly insuperable difficulties in connection with 

 this problem. 



As for the very prevalent notions that Ammonites and Belem- 

 nites, Trigonise and Brachiopods, with Ichthyosaurs, Pliosaurs, 

 and Plesiosaurs, could only have lived in warm, if not actually 

 tropical, climates, I know of no grounds whatever for any such 

 belief. The nearest living allies of the invertebrates referred to 

 flourish at considerable depths in icy-cold water ; and, seeing that 

 large marine mammals now live amid snow and ice, I cannot 

 understand why the great marine reptiles might not have done the 

 same. Just as little reason is there for inferring that Sigillarids, 

 Lepidodendrids, and Calamites could only have lived in 

 tropical jungles, as there is for the once popular notion that they 

 flourished in an atmosphere supplied with a very exceptional 

 proportion of carbonic acid ! 



The sooner geologists recognize the fact that all our ideas con- 

 cerning the distribution of the forms of marine life have been 

 completely revolutionized by the discovery that there are cold 

 and dark abysses, which are tenanted by numerous organisms 

 having many affinities with those which live in shallow water, 

 warmed by a tropical sun and flooded with light, the more likely 

 will they be to avoid the errors into which we have fallen in the 

 past. Not until the exact distribution of life- forms at different 

 depths in the ocean has been much more perfectly worked out 

 than it has been at present, will it be safe to reason with any 

 confidence concerning the distribution of extinct types ; and, even 

 then, we shall ever have to be on our guard against the prevalent 

 fallacy which assumes that analogies in structure are indicative of 

 similarities in the conditions of life. 



And here it may be remarked that the imperfect methods 

 employed on board the Challenger and most other surveying 

 ships leave almost everything yet to be done in the way of 

 determining the limits of depth, temperature, pressure, and other 

 conditions under which the different forms of marine life can 

 flourish. It is much to have obtained so great an insight into 

 the characters of some of the creatures inhabiting the deepest 

 parts of the ocean, and of the peculiar conditions which must 

 exist in some of those places where marine life is abundant. But 

 the work which has yet to be done requires the employment of 

 dredges and nets which can be opened when they have reached 

 a certain depth in the ocean, and which can be closed again 

 before being drawn to the surface. Only by the employment of 

 such apparatus can we hope to avoid those sources of error which 

 viuate all our present generalizations concerning the bathy- 

 metrical distribution of the existing forms of marine life. 



When, in addition to these biological studies, we have equally 

 careful determinations of the physical characters of deposits 

 formed at varying depths and distances from the shore, and under 

 diverse influences of tides and currents, we may hope, by com- 

 bining the physical and biological eviilence, to arrive at some- 

 thing like certain conclusions concerning the exact conditions 

 under which various geological formations have been accumu- 

 lated ; for at present our speculations upon the subject are often 

 little better than haphazard guesses. 



Thi conditions which must have prevailed during the depo- 

 sition of a particular bed having been determined, the present 

 mineral condition of the organic remains becomes a subject of 

 very interesting study ; for here we may find a clue which will 

 enable us to unravel the series of physical and chemical changes 

 which must have gone on in the mass, since the first accumula- 

 tion of its materials. In cases of difficulty of this kind, the 

 condition of alteration of a shell or bone, of which the original 

 composition is known, becomes an especially valuable piece of 

 evidence. 



I am convinced that the future progress of geological thought 

 is closely bound up with the increase of our knowledge concern- 

 ing the conditions under which the various forms of marine life 

 flourish, and under which their remains become embedded in 

 sedimentary deposits ; though what has been already accom- 

 plished in this direction, it must be admitted, is but small, and 

 much of it will have to be done over again. 



