September 24, 1896J 



NA rURE 



495 



UnowlL'dfje of earth-history ; but it must be remembered that 

 the imperfection of the physical record is equally striking, as 

 will be insisted on more fully in the sequel. 



Specially prominent amongst the points upon which we are 

 ignorant stands the nature of the Precambrian faunas. The 

 extraordinary complexity of the earliest known Cambrian fauna 

 has long been a matter for surprise, and the recent discoveries 

 in connection with the Olciullus fauna do not tliminish the feel- 

 ing.' After commenting upon the varied nature of the earliest 

 known fauna, the late I'rof. Huxley, in his Address to the 

 ('■eoliigical Society in 1862. stated that " any admissible hypo- 

 thesis of progressive modil'icatiim must be compatible with 

 persistence without progression, through indefinite periods. . . . 

 Should such an hypothesis eventually be proved to be true, . . . 

 the conclusion will inevitably present itself, that the PaUeozoic, 

 Mesozoic, and Cainozoic fauna; and flora', taken together, bear 

 .somewhat the same proportion to the whole .series of living 

 beings which have occupied this globe, as the existing fauna and 

 flora do to them." Whether or not this estimate is correct, all 

 geologists will agree that a vast period of time must have elap.sed 

 before the CanUjrian period, and yet our ignorance of faunas 

 cxi.sting prior to the time when the OiciicUiis fauna occupied 

 the Cambrian seas is almost complete. True, many Precambrian 

 fossils have been described at various times, Init, in the opinion 

 of many competent judges, the organic nature of each one of 

 these requires confirmation. I need not, however, enlarge upon 

 this matter, for I am glad to say we have amongst us a geologist 

 who will at a later stage read a paper before this Section upon 

 the subject of Precambrian fo.ssils, and there is no one better 

 able, owing to his intimate acquaintance with the actual relics, 

 to present fairly and impartially the arguments which have been 

 advanced in favour of the organic origin of the objects which 

 have been appealed to as evidences of organisms of Precambrian 

 age than our revered co-worker from Canada, Sir J. William 

 Dawson. We may look forward with confidence to the future 

 discovery of many faunas older than those of which we now possess 

 certain kiiowledge, but until these are discovered, the paU\;onto- 

 logical record must be admitted to be in a remarkably incomplete 

 condition. In the meantime, a study of the recent advance of our 

 knowledge of early life is significant of the mode in which still 

 earlier faunas will probably be brought to light. In 1845, ^'■• 

 E. Emmons described a fossil, now known to be an Olciu-lliis, 

 ihcnigh at that time the earliest fauna was supposed to be one 

 containing a much later group of organisms, and it was not 

 until Nalhorst and Hrbgger established the position of the 0/e- 

 itclliis zone that the existence of a fauna earlier than that of 

 which I\iradoxides was a member was admitted ; and, indeed, 

 the Paradoxides i^wca^ itself was proved to be earlier than that 

 containing Olenus, long after these two geflera had been made 

 familiar to |Kila;onlologists, the Swedish paleontologist, Augelin, 

 having referred the J'aradoxides fauna to a period earlier than 

 tliat of the one with OUiiiis. It is quite possible, therefore, that 

 fossils are actually preserved in our museums at the present 

 moment, which have been extracted from rocks deposited before 

 the period of formation of the OlciieUus beds, though their age 

 has not been determined. The Olciiclliis horizon now furnishes 

 us with a datum-line from which we can work backwards, and it 

 is quite possible that the Neoholus beds of the Salt Range,- 

 whicb underlie beds holding Ohiullus, really do contain, as has 

 been maintained, a fauna of date anterior to the formation of 

 the OUiicllus beds ; and the same may be the case with the beds 

 containing the Protolcniis fauna in Canada,^ for this fauna is 

 very ditVerent from any known in the Olciullus beds, or at a 

 higher horizon, though Mr. G. F. Matthew, to whom geologists 

 owe a great debt for his admirable descriptions of the early 

 fossils of the Canadian rocks, speaks very cautiously of the age 

 of the beds containing ProloUnits and its associates. Not- 

 withstanding our ignorance of Precambrian faunas, valuable 

 work has recently been done in proving the existence of im- 

 portant groups of stratified rocks deposited previously to the 

 formation of the beds containing the earliest known Cambrian 



1 Dr. C. D. Walcotl, in his monograph on " The Fauna of the Lower 

 Ca.n)hrian or OlencUus Zone ■' (Washington 1890), records the following 

 great groups as lepresented in the Olenellus beds of America : — Spongiie, 

 Hydro/t>a, Actinozoa, Echinodermata, AnnelidaV (trails, burrows, and 

 tracks), r.rachiopoda, Lamellibrancliiata, Gasteropoda, Pteropoda, Crus- 

 tacea, and Trilobita. Others are known as occurring in beds of the same 

 age in the Old World. 



-Sec F. Noelling, "On the Cambrian Formation of the Eastern Salt 

 Range." Records Geot. Sun'^y^ India^ vol. xxvii. p. 7 



3G. F. M.itlhew, '■The Protolenus Fauna." Tram 

 of Science, 1895, vol. xiv. p. 101. 



NO. 1404, VOL. 54] 



Ne-M York Acad. 



fo.ssils ; I may refer especially to the proofs of the Precambrian 

 age of the Torridon sandstone of north-west Scotland, lately 

 furnished by the officers of the (leological Survey, and their 

 discovery that the maximum thickness of these strata is over 

 10,000 feet.' Amongst the sediments of this important system, 

 more than one fauna may be discovered, even if most of the 

 strata were accumulated with rapidity, and all geologists must 

 hope that the officers of the .Survey — who, following Nicol, Lap- 

 worth, and others, have done so much to elucidate the geological 

 .structure of the Scottish Highlands — may obtain the legitimate 

 reward of their labours, and definitely prove the occurrence of 

 rich faunas of Precambrian age in the rocks of that region. 



But, although we may look forward hopefully to the time when 

 we may lessen the imperfection of tlie records of early life upon 

 the globe, even the most hopeful cannot expect that record to be 

 rendered perfect, or that it will make any near approach to per- 

 fection. The posterior segments of the remarkable trilobite 

 Mcsoimcis vernioittana are of a much more delicate character 

 than the anterior ones, and the resemblance of the spine on the 

 fifteenth " body-segment " of this species to the terminal spine 

 of Olciullus proper, suggests that in the latter sub-genus pos- 

 terior segments of a purely membranous character may have 

 existed, devoid of hard parts. If this be so, the entire outer 

 covering of the trilobites, at a period not very remote from the 

 end of Precambrian times, may have been membranous, and the 

 same thing may have occurred with the structures analogous to 

 the hard parts of organisms of other groups. Indeed, with our 

 present views as to development, we can scarcely suppose that 

 organisms acquired hard parts at a very early period of their exist- 

 ence, and fauna after fauna may have occupied the globe, and 

 disappeared, leaving no trace of its existence, in wliich case we 

 are not likely ever to obtain definite knowledge of the char- 

 acters of our earliest faunas, and the biologist must not look to 

 the geologist for direct information concerning the dawn of life 

 upon the earth. 



Proceeding now to a consideration of the faunas of the rocks 

 formed after Precambrian times, a rough test of the imperfection 

 of the record may be made by examining the gaps which occur 

 in the vertical distribution of forms of life. If our knowledge 

 of ancient faunas were very incomplete, we ought to meet with 

 many cases of recurrence of forms after their apparent disappear- 

 ance from intervening strata of considerable thickness, and many 

 such cases have actually been described by that eminent palaeon- 

 tologist, M. Barrande, amongst the Pakeozoic rocks of Bohemia, 

 though even these are gradually being reduced in number owing 

 to recent discoveries ; indeed, in the case of the marine faunas, 

 marked cases of recurrence are comparatively rare, and the 

 occurrence of each form is generally fairly unbroken from its 

 first appearance to its final extinction, thus showing that the im- 

 perfection of the record is by no means so marked as might be 

 supposed. Fresh-water and terrestrial forms naturally furnish a 

 large percentage of cases of recurrence, owing to the comparative 

 rarity with which deposits containing such organisms are pre- 

 served amongst the strata. 



A brief consideration of the main reasons for the present im- 

 perfection of our knowledge of the faunas of rocks formed sub- 

 sequently to Precambrian times may be useful, and suggestive ot 

 lines along which future work may be carried out. That detailed 

 work in tracts of country which are yet unexplored, or have 

 been but imperfectly examined by the geologist, will add largely 

 to our stock of information, needs only to be mentioned ; the 

 probable importance of work of this kind in the future may be 

 inferred from a consideration of the great increase of our know- 

 ledge of the Permo-Carboniferous faunas, as the result of recent 

 labours in remote regions. It is specially desirable that the 

 ancient faunas and floras of tropical regions should be more fully 

 made known, as a study of these will probably throw consider- 

 able light upon the influence of climate upon the geographical 

 distribution of organisms in past times. The old floras and 

 faunas of Arctic regions are becoming fairly well known, thanks 

 to the zeal with which the Arctic regions have been explored. 

 But, confining our attention to the geology of our own couiitry, 

 much remains to be done even here, and local observers especially 

 have opportunities of adding largely to our stock of knowledge, 

 a task they have performed so well in the past. To give examples 

 of the value of such work, our knowledge of the fauna of the 

 Cambrian rocks of Britain is largely due to the present President 

 of the Geological Society, when resident at St. David's, whilst 



1 Sir A. Geikie, " Annual Report of the Geological Survey [United 

 Kingdom] ... for the year ending December 31, 1893." (London, 1894.) 



