Septemher 24, 1896] 



NA TURE 



^99 



ward circumslances, wnukl spieud furllier laterally llian llicy 

 now del ; but as we know that in earliest Cambrian times the 

 diversity of organisation was very considerable, it is doubtful 

 whether any appreciable difference would be exerted upon 

 lateral distribution then and now, owing to this cause. At the 

 time at which Pictet wrote, the rich fauna of the deeper parts 

 of the oceans, with its many widely distributed forms of life, was 

 unknown, and the range in space of early organisms must have 

 then struck every one who thought upim the subject as being 

 greater than that of the shallow-water organisms of existing 

 seas, which were alone know n. It is by no means clear, however, 

 with our present knowledge, that Pictet's supposed law holds 

 good, and it will rei)uire a considerable amount of work before 

 it can be shown to be even apparently true. Our lists of the 

 fossils of different areas are not sufficiently complete to allow us 

 to generalise with safety, but a comparison of the faunas of 

 Australia and Hritain indicates a larger percentage of forms 

 common to the two areas, as we examine higher groups of the 

 geological column. If this indication be fully borne out by 

 further work, it will not prove the actual truth of the law, for 

 the apparent wider distribution of ancient forms of life might be 

 due to the greater probability of elevation of ancient deep-sea 

 sediments than of more modern ones which have not been 

 subjected to so many elevatory movements. Still, if the law be 

 apparently true, it is a matter of some importance to geologists ; 

 and I have touched upon the matter here in order once again to 

 emphasise the possibility of correlating comparatively small 

 thicknesses of strata in distant regions by their included 

 organisms. 



Mention of Pictet's laws, one of which states that fossil 

 animals were constructed upon the same plan as existing ones, 

 leads me to remark upon the frequent assumption that certain 

 fossils are closely related to living groups, when the resemblances 

 between the hard parts of the living and extinct forms are only 

 of the most general character. There is a natural tendency to 

 compare a fossil with its nearest living ally, but the comparison 

 has probably been often pushed too far, with the result that 

 biologists have frequently been led to look for the ancestors of 

 one living group exclusively amongst forms of life which are 

 closely related to those of another living group. The result of 

 detailed work is to bring out more and more prominently the 

 very important differences between some ancient forms and any 

 living creature, and to throw doubts on certain comparisons ; 

 thus I find .several of the well-known fossils of the Old Red 

 .Sandstone, formerly referred without hesitation to the fishes, are 

 now doubtfully placed in that class. 



The importance of detailed observation in the field is becoming 

 every day more apparent, and the specialist who remain.s in his 

 museum examining the collections amassed by the labours of 

 others, and never notes the mode of occurrence of fossils in the 

 strata, will perhaps soon be extinct, himself an illustration of the 

 principle of the survival of the fittest. In the first place, such a 

 worker can never grasp the true .significance of the changes 

 wrought on fossil relics after they have become entombed in the 

 strata, especially amongst those rocks which have been subjected 

 to profound earth-movements : and it is to be feared that many 

 "species "are still retained in our fossil li.sts, whose supposed 

 .specific characters are due to distortion by pressure. I3ut a 

 point of greater importance is, that one who confines his atten- 

 tion to museums, cannot, unless the information supplied to 

 him be very full, distinguish the diflerences between fossils which 

 are variations from a contemporaneous dominant form, such as 

 " sports,'' and those which have been termed " mutations," 

 which existed at a later period than the forms which they 

 resemble. The value of the latter to those who are attempting 

 to work out phylogenies is obvious, and their nature can only be 

 determined as the result of very laborious and accurate field- 

 work ; but such labour in such a cause is well worth performing. 

 The student of phylogeny has had sufficient warning of the 

 dangers which beset his path, from an inspection of the various 

 phylogenelic trees, constructed mainly after study of existing 

 beings only, so 



"... like the Itorealis race. 

 That flit ere you can point their place," 



but recent researches amongst various groups of fossil organisms 

 have further illustrated the danger of theorising upon insufficient 

 data, especially suggestive being the discovery of closely similar 

 forms which were formerly considered to be much more neatly 

 related than now proves to be the case ; thus Dr. Mojsisovics 

 (Abhaiidl. der k. k. geol. Keuhsanst., vol. vi., 1893) has shown 



N(J. 1404, VOL. 54] 



that Ammonites once referred to the same species are specifically 

 distinct, though their hard parts have acquired similar structures, 

 sometimes contemporaneously, sometimes at different times, and 

 Mr. S. S. Buckman {Quart. Jour 11. Gcol. Soc, vol. li. p. 456, 

 1S95) has observed the same thing, which he speaks of as 

 ■' heterogenetic homceomorphy " in the case of certain 

 brachiopods, whilst Prof. H. A. Nicholson and I (Geo/, ^/ag., 

 December 4, 1895, ^'o'- "• P- 5^0 have given reasons for 

 supposing that such heterogenetic homreomorphy, in the case of 

 the graptolites, has sometimes caused the inclusion in one genus 

 of forms which have arisen from two distinct genera. As the 

 result of careful work, dangers of the nature here suggested will 

 be avoided, and our chances of indicating lines of descent 

 correctly will be much increased. It must be remembered that 

 however plausible the lines of descent indicated by students of 

 recent forms may be, the actual links in the chains can only be 

 discovered by examination of the recks, and it is greatly to be 

 desired that more of our geologists, who have had a thorough 

 training in the field, should receive in addition one as thorough 

 in the zoological laboratory. Shall I be forgiven if I venture on 

 the opinion that a certain suspicion which some of my zoological 

 fellow countrymen have of geological methods, is due to their 

 comparative ignorance of paleontology, and that it is as 

 important for them to obtain some knowlerlge of the principles 

 of geology as it is for the stratigraphical pakeontologist to study 

 the soft parts of creatures whose relatives he finds in the 

 stratified rocks ? 



The main lines along which the organisms of some of the 

 larger groups have been developed, have already been indicated 

 by several paleontologists, and detailed work has been carried 

 out in several cases. As examples, let me allude to the trilo- 

 bites, of which a satisfactory natural classification was outlined 

 by the great Barrande in those volumes of his monumental work 

 which deal with the fossils of this order, whilst further indica- 

 tion of their natural inter-relationships has been furnished by 

 Messrs. C. D. Walcott, G. F. Matthew, and others ; to the 

 graptolites, whose relationships have been largely worked out 

 by Prof. C. Lapworth, facile priitceps amongst students of the 

 Grapioliloidca, to whom we look for a full account of the 

 phylogeny of the group ; to the brachiopods, which have been 

 so ably treated by Dr. C. E. Beecher ("Development of the 

 Brachiopoda," Amcr. Jount. Sit., ser. iii. vol. xli. (1891) 

 p. 343, and vol. xliv. (1S92) p. 133), largely from a study of 

 recent forms, but also after careful study of those preserved in 

 the fossil state ; and to the echinids and lamellibranchs, whose 

 history is being extensively elucidated by Dr. R. T. Jackson 

 (" Phylogeny of the Pelecypoda," J/cw. Boston Soc. Nat. Hist., 

 vol. iv. (1890) p. 277 ; and " Studies of Palaeechinoidea," Bull. 

 Gcol. Soc. Amer., vol. vii. (1896) p. 171), by methods some- 

 what similar to those pursued by Dr. Beecher. I might give 

 other instances,' but have chosen some striking ones, four of 

 which especially illustrate the great advances which are being 

 inade in the study of the p.ileontology of the invertebrates by 

 our American brethren. 



I have occupied the main part of my address with reasons for 

 the need of conducting stratigraphical work with minute 

 accuracy. Many of you may suppose that the necessity for 

 working in this way is so obvious that it is a work of supere- 

 rogation to insist upon it at great length ; but experience has- 

 taught me that many geologists consider that close attention to 

 details is apt to deter workers from arriving at important 

 generalisations, in the present state of our science. A review 

 of the past history of the science shows that William Smith, and 

 those who followed after him, obtained their most important 

 results by steady application to details, and subsequent generali- 

 sation, whilst the work of those who theorise on insufficient 

 data is apt to be of little avail, though often demanding atten- 

 tion on account of its very daring, and because of the power of 

 some writers to place erroneous views in an attractive light, 



just as 



"... the sun can fling 

 Colours as bright on exhalations bred 

 By weedy pool or pestilential swamp, 

 As on the rivulet, sparkling where it runs. 

 Or the pellucid lake." 



1 E.g. The following papers treating of the Cephalopoda :— A. Hyatt, 

 " Genesis of the Arielida;," Smithsonian Contributions, vol. .vxvi. (1889); 

 M. Neumayr, Jura-Studien I., "Ueber Phylloceraten,"/rt/rr^. der k. k. 

 Gcol. Reichsaiist , vol. x.vi. (1871) p. 297 \ L- Wunenberger. " Studien iibe 

 die Slammesgeschichte der Ammoniten," Leipzig, 1880; S. S. Buckman. 

 " A Monograph of the Inferior Oolite Ammonites of the British Islands, ' 

 1887 (.Monogr. Palaontograplikal Sec). 



