426 



NATURE 



[March i, 1888 



We hear much — far too much, as I think — at the present day 

 of an "irrational unifomiitarianism." Is not the real source of 

 danger in an exactly opposite direction? Does not the irration- 

 ality characterize him who, without attempting to obtain a more 

 complete knowledge of the processes going on during the original 

 deposition and subsequent changes of rock-masses, is ready, as 

 each new difficulty presents itself, to fall back upon soaae old 

 discredited Dens ex machina in the form of deluges of water, 

 floods of fire, boiling oceans, caustic rains, or acid-laden 

 atmospheres ! 



Considering how little we as yet know of many of the con- 

 ditions under which deposits are being formed at the present 

 day, and remembering how large a part of the little we do know 

 has been acquired only within the last few years, we might pause 

 before declaring that the path upon which geology entered in 

 earnest only some fifty years ago is a wrong one, and that the 

 sooner we begin to retrace our steps the better. 



Can we even now be in danger of forgetting that " Slough of 

 Despond," wherein the geologist, laden with a grievous burden 

 of traditional assumptions and irrational theories, so hopelessly 

 floundered, till one Help pointed out a way of escape, and sent 

 him on his way rejoicing, with the " Principles of Geology " in 

 his hand ? 



The second aspect in which paJKontological science presents 

 itself to the geologist, is as affording a key to the chronology of 

 the rock-masses of the globe. We still regard fossils as the 

 "medals of creation," and certain types of life we take to be 

 as truly characteristic of definite periods as the coins which bear the 

 image and superscription of a Roman emperor or of a Saxon king. 



But in the application of the principle that " strata are to be 

 identified by their organic remains," we have now to admit as 

 many limitations, and to exercise as much caution, as when 

 judging of the conditions under wliich rock-masses must have 

 been deposited, from the characters of the fossils which they 

 contain. 



With the restricted area of the south-west of England, where 

 William Smith achieved his epoch-making discovery, the doc- 

 trine which he announced seemed to be absolutely true ; each 

 formation exhibited a paculiar and perfectly characteristic assem- 

 blage of organic remains, by means of which it could at once be 

 recognized. The still more detailed studies of strata of the 

 same age, by Hunton and Williamson in Yorkshire, by Marcou 

 in the Jura, and by Quenstedt in Swabia, seemed to show that the 

 principle had a wider application than even its author himself 

 could have imagined, and that zones a few feet or even inches 

 in thickness might be followed over considerable districts,- every- 

 where marked by some particular type of Ammonite or other 

 charactei'istic fossil. 



But the more thorough and systematic study of corresponding 

 formations over wide areas, which was inaugurated by Oppel, 

 and has been carried on by many palteontologists since, has 

 abundantly demonstrated that, striking as is the parallelism of 

 the zones in such a formation as the Lias, when studied in 

 England, France, and Germany, yet the species and varieties 

 found on the same horizon at distant points are in many cases 

 not identical, but merely representative ; and, further, that as we 

 pass away from any typical area, the sharp distinction between 

 the several zones ^eems gradually to vanish. 



The same facts come out very strikingly when we study any 

 other great geological period. In the oldest fossiliferous strata, 

 those of the Cambrian, nothing can be more striking than the 

 similarity of the faunas in North America, Britain, Scandinavia, 

 and Bohenaia ; and yet the species which occur at the several 

 different horizons in these countries are certainly, for the most 

 part, not identical, but only i-epresentative. No fact, it seems 

 to me, could more clearly indicate that, even at that early 

 period, there were life-provinces with a distribution of or- 

 ganisms in space quite analogous to that which exists at the 

 present day. 



To pass to slightly younger rocks. What can be more striking 

 than the evidence of the limits of two life-provinces, afforded by 

 the Calciferous strata of North America and the similar rocks of 

 Scotland and Northern Europe, which contain the remarkable 

 Maclureas and a peculiar assemblage of Cephalopods and other 

 fossils ; for these are seen at Girvan to coma into close 

 contiguity with the more southern type of Silurian, containing a 

 very different fauna, so well seen in the Lake District and North 

 Wales. 



Another striking example of the same kind is afforded by the 



Cretaceous, of which the Southern type, marked by the abund- 

 ance of Hippurites, Orbitolites, and other remarkable forms, 

 comes into close relations, as has been so well shown by Hebert, 

 with the type which yields the ordinary Cretaceous fauna of 

 Central Europe. In these and siinilar cases which might be 

 mentioned we trace the existence of two approximating marine 

 provinces, like those which at the present day are separated by 

 the Isthmus of Panama. 



Profs. Neumayr and Mojsisovics have indeed shown that there 

 are good causes for believing that the distinction between the 

 marine zoological provinces in Triassic and Jurassic times was at 

 least as clearly marked as between the similar provinces of the 

 present day ; and the former naturalist has in addition pointed 

 out that within the geographical provinces we have also very 

 recognizable climatic zones. 



In the year 1862, Prof. Huxley, speaking from this chair, 

 uttered a much-needed warning against the growing practice 

 among palaeontologists of treating geological equivalence as 

 meaning the same actual contemporaneity ; and against the 

 assumption, without positive proof, that ancient faunas and 

 floras had an indefinite and even world-wide distribution. 

 Palseontological discoveries during the last quarter of a century 

 in Western North America, in India, in the Cape Colony, 

 Australia, and New Zealand, have abundantly justified these 

 cautions, and have shown how much such a term as "homo- 

 taxis" is needed, in order to guard against errors resulting from 

 the abuse of the phrase " geological contemporaneity." 



But when Prof. Huxley went on to suggest that "a, Devonian 

 fauna and flora in the British Isles may have been contem- 

 poraneous with Silurian life in North America and with a 

 Carboniferous fauna and flora in Africa," I think that geo- 

 logists, with the evidence they have now before them, must take 

 exception to so sweeping a generalization. Finding, as we do, 

 on both sides of the Atlantic the same succession of Cambrian, 

 Ordovician, Silurian, Devonian, and Carboniferous strata, con- 

 taining strikingly representative, if not identical faunas, it is 

 impossible to doubt their general parallelism ; however ready 

 we may be to admit that the migration or development of new 

 forms of life in the two areas need not have occurred synchron- 

 ously, and that thus a certain amount of overlapping of the 

 periods represented at distant points by the same system may 

 exist. 



On the other hand, I believe that the study of fossils from 

 remote parts of the earth's surface has abundantly substantiated 

 Prof. Huxley's alternative suggestion that "geographical pro- 

 vinces and zones may have been as distinctly marked in the 

 Palaeozoic epoch as at present." The ever-accumulating mass 

 of palaiontological evidence seems to me to be all pointing in 

 this direction ; and I confidently anticipate that the paloeonto- 

 logical anomalies which in the past have caused so much doubt 

 and difficulty, will, by the establishment of this principle, 

 receive a full and satisfactory explanation. 



As long ago as 1846, Darwin, in his " Observations on South 

 America," showed that certain assemblages of fossils presented 

 a blending of characters, which in Europe are only found apart 

 in faunas which are of Jurassic and Cretaceous age respectively. 

 Since that date, the study of the fossil faunas and floras of South 

 Africa, India, Australia, New Zealand, and the Western Terri- 

 tories of North America has furnished an abundance of facts of 

 the same kind, showing that no classification of geological 

 periods can possibly be of world-wide application : that we must 

 be contented to study the past history of each great area of the 

 earth's surface independently, and to wait patiently for the evi- 

 dence which shall enable us to establish a parallelism between 

 the several records. Attempts to establish a universal system 

 of nomenclature or classification of sedimentary rocks are indeed 

 greatly to be deprecated, for if the zoological and botanical dis- 

 tribution of past geological times were at all comparable to 

 that of the present day, any such universal system must be 

 impossible. 



The suggestion made to this Society by Prof. Huxley at a 

 somesvhat later date is equally valuable and important. Refer- 

 ring to the fauna of the Trias, he said : — " It does not appear 

 to me that there is any necessary relation between the fauna of 

 a given land and that of the seas of its shores. At present our 

 knowledge of the terrestrial faunse of past epochs is so slight 

 that no practical difficulty arises from using, as we do, sea- 

 reckoning for land-ti»ne. But I think it highly probable that, 

 sooner or later, the inhabitants of the land will be found to have 

 a history of their own." 



