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at the same time as steadily accumulating material for sound geological knowledge. Before Forbes' time, little was known of the invertebrata of deep waters. The systems of stratified, fossil-bearing rocks had been determined from really insufficient data. Almost nothing was known of marine invertebrata, that is to say, of sea-living animals of three of the four great branches of the animal kingdom except the littoral and shoal-water species.
Werner's rude conception, the first attempt to explain the formation of strata, was succeeded by Hutton's more rational theory. Out of this, substantially, modern geology has been gradually evolved. One of its earliest accepted doctrines was, that continuous strata were deposited, one after another, over the entire surface of the earth. Thus its crust was believed to be made up of concentric layers, each of which was supposed to be throughout one in mineral composition, and to be underlaid by older and overlaid by newer ones of different mineral characters. It was possible then to identify strata only by lithological character and order of superposition. As soon as the rising science of palæontology made known the importance of fossils to the geologist, they were recognized as affording a third key to the knowledge of formations. Forthwith every writer on the science put on record this dogma, that fossiliferous strata are to be distinguished among themselves by three things: order of superposition, mineral composition, and organic remains. It was soon, however, found that for districts widely separated, superposition proved nothing, and that for even limited areas its evidence could be received only with the greatest caution, and that the testimony of mineral character was even less reliable. Hence, while all textbooks of geology written twenty years ago paraded the three keys of identification as valid, it was always with such after tatements as left on the mind of the student the impression that, after all, to quote the language of one of the best of those books, “identification of formations," emphasized by italics, “consists in identification of fossils."1
It was also assumed that climatic and other conditions, and the fauna and flora of the earth, were very similar in all parts. This was supposed to be the state of things up to the middle of the tertiary period, when the former equable sub-tropical climate changed to one colder than those of the present era, and which first led to the distribution of life in zones. And such is very nearly the teaching of the standard authorities on general palæontology to this day, as the
1 Loomis' Elements of Geology, p. 62.
reader of the excellent, and, as Agassiz styles it," "classical work,” of Pictet, ? is aware.
This was essentially the state of opinion, when Forbes first cast dredge into the waters of his native Isle of Man. Presently he began to define zones of 'depth, characterized by distinct assemblages of animals, analagous to the zones of animal and plant life upon the land, already recognized by naturalists and marked by latitude or altitude. By his dredgings in the Ægean sea, in 1841, he reached depths never before explored, and there discovered abundant life, where it had been assumed to be wholly wanting. He wrote home to England:3 "I have found a defined fauna different from any other of the marine zones, between ninety and two hundred fathoms in these seas. ... I have found star-fishes at two hundred fathoms. ... Moreover, the most characteristic shells of this hitherto unknown region are only known to conchologists as fossil. I only have seen them alive and kicking.' Though he penetrated to no greater depth than two hundred and thirty fathoms, he found data for a conclusion, which, with the impression it made, will be best conveyed in his own words, taken from a letter, dated March, 1846. He says: “I have just terrified the geologists by maintaining at their meeting that the identity of fossils in strata geographically far apart, must lead to the inference that the beds were of different, not, as hitherto maintained, of the same age." He never retracted this opinion up to his death in 1854.
Yet it should here be said that De la Beche had before arrived at a similar conclusion from other data. But his reasonings on this point had produced little effect on geologists, else they could not have been so startled by Forbes' communication. This chanced to meet my eye at an early period of my work as a teacher. Struck with the force of the objection to the common view, and not till some years after aware of De la Beche's like opinion, which had been published in a work never much known in this country, as his "Geological Observer” has been, I watched the effect of Forbes' heresy upon geological writers. Were that effect measured by the direct notice his opinion has received from the chief authorities in the science, it would be set down as zero; for it is a singular fact that no edition of Lyell's “Elements,” or “ Principles," nor the “Manual" of Dana has
1 Essay on Classification,
anywhere distinctly quoted or recognized the objection, though all these works frequently introduce Forbes' observations and views on other important points. Yet the careful observer will not find evidence wanting that the seed sown has borne fruit. He will find guarded and qualified statement on the matter of identification. Thus in the last editions of Lyell's “ Elements,” the latest bearing date of December, 1870, the author writes thus:1 “Organic remains must be used as a criterion of the age of a formation, or of the contemporaneous origin of two deposits in distant places, under much the same restriction as the test of mineral composition.” Prof. Dana, of whose world-wide reputation in geology, mineralogy, and zoology, Americans may well be proud, remarks in his “Manual,"? “Identity of species of fossils proves approximately identity of age" of strata. Jukes, the friend of Forbes, and his colleague in the British Geological Survey, alone speaks in explicit terms, in his “Manual,"3 of the difficulty in determining the contemporaneity of distant formations by their fossils; but he does not take the strong ground of Forbes.
Forbes did not leave on record the process by which he reached his conclusion. But knowing that he believed, that in every age, there have existed sea and dry land, and that consequently areas of subsidence must have been, as they are now, always limited; and holding besides as he did, and as most of us still do, the doctrine of single specific centres, it is easy to conceive why to him identity of fossils in widely separated regions indicated only that at certain periods their conditions had been so similar as to fit them to support like forms of life, and that those periods, instead of being one and the same, were probably very far apart. In short, he maintained that indentity of fossils implied identity of conditions, nothing more.
That we may not seem presumptuous in our further remarks on this delicate subject, let us employ, as far as possible, the testimony of men who are leaders in their respective departments. Indeed, but for the fact that the published views of two eminent English authors are now easily accessible to American readers, we should have kept silence upon the relations of geology to its theories. These writers recognize and maintain Forbes' objection, though but one of them alludes to him by name; and to a certain extent they show the consequences it entails.
Herbert Spencer's essay on “Illogical Geology," originally issued in an English quarterly, was republished in this country in 1864, and has therefore been long before the public. Prof. Huxley's
1 Students' Elements of Geology: London, 1871, p. 102.
3 P. 407.
address to the Geological Society of London, on “Geological Contemporaneity and Persistent Types of Life,” though delivered in 1862, was only last autumn, with the author's revision, republished at home and here in book form, with other articles making up the now famous volume entitled "Lay Sermons, Addresses and Reviews.”' Both authors emphatically object to what we have termed the leading theory of geology, as insufficient in its basis. A few brief and expressive passages will sharply define their position as to this and related points.
Spencer begins with showing by clear examples from geological writers, “the way in which the science is still swayed by the crude hypothesis it set out with; so that even now, old doctrines that are abandoned as untenable in theory, continue in practice to mould the ideas of geologists, and to foster sundry beliefs that are logically indefensible.”] He quotes extracts from Murchison's "Siluria,” which absolutely prove that after the author had, by his own confession, been misled in respect to age of formations by relying on the old criterion of mineral character, he was yet governed in subsequent decisions by a "latent belief” in the worthless and rejected test. Spencer well remarks: "Is it not manifest, then, that the exploded hypothesis of Werner continues to influence geological speculation."
He comes next to the subject of groups of strata. The following are his own words :
The Silurian system, the Devonian system, the Carboniferous system, etc., are set down in our books as groups of formations which everywhere succeed each other in a given order; and are severally everywhere of the same age. Though it may not be asserted that these successive systems are universal, yet it seems to be tacitly assumed that they are so. In North and South America, in Asia, in Australia, sets of strata are assimilated to one or other of these groups; and their possession of certain mineral characters and a certain order of superposition, are among the reasons assigned for so assimilating them. Though, probably, no competent geologist would contend that the European classification of strata is applicable to the globe as a whole, yet most, if not all geologists write as though it were so. Among readers of works on geology, nine out of ten carry away the impression that the divisions of primary, secondary, and tertiary are of absolute and uniform application; that these great divisions are separable into sub-divisions, each of which is definitely distinguished from the rest, and is everywhere recognizable by its characters as such or such; and that in all parts of the earth, these minor systems severally began and ended at the same time.'
1 Illustrations of Universal Progress, p. 311.
3 Ib., p. 335.
He adds: “Now this belief that geologic'systems' are universal is quite as untenable as the other. It is just as absurd when considered á priori; and it is equally inconsistent with the facts."1 Having adduced clear cases in support of his position, he remarks: “Yet so strongly is geological speculation swayed by the tendency to regard the phenomena as general instead of local, that even those most on their guard against it seem to be unable to escape its influence."'? He quotes an earnest protest of Lyell against this bias, a part of which is as follows: “It was in vain to urge as an objection the improbability of the hypothesis which implies that all the moving waters on the globe were once simultaneously charged with sediment of a red color,"3 in accounting for the deposition of the red sandstones and marls.
And yet Spencer declares that notwithstanding this and numerous passages of like implication, Lyell seems himself not to be free from the bias, and proceeds to say :
Though he utterly rejects the old hypothesis that all over the earth the same continuous strata lie upon each other in regular order, like the coats of an onion, he still writes as though geologic "systems" do thus succeed each other. A reader of his "Elements” would certainly suppose him to believe that the primary epoch ended and the secondary epoch commenced all over the world at the same time,-that these terms really correspond to distinct universal eras in nature.
Lastly, Spencer takes up, to use his own words :
The doctrine that strata of the same age contain like fossils, and that, therefore, the age and relative position of any stratum may be known by its fossils. While the theory that strata of like mineral characters were everywhere deposited simultaneously has been ostensibly abandoned, there has been accepted the theory that in each geologic epoch similar plants and animals existed everywhere; and that, therefore, the epoch to which any formation belongs may be known by the organic remains contained in the formation. Though, perhaps, no leading geologist would openly commit himself to an unqualified assertion of this theory, yet it is tacitly assumed in current geological reasoning. This theory, however, is scarcely more tenable than the other. It cannot be concluded with any certainty, that formations in which similar organic remains are found, were of contemporaneous origin; nor can it be safely concluded that strata containing different organic remains are of different ages. To most readers these will be startling propositions ; but they are fully admitted by the highest authorities. Sir Charles
1 Illustrations of Universal Progress, p. 336.