THE

GEOLOGICAL MAGAZINE.

BY

NEW SERIES. DECADE II. VOL. VI, IBRAIN

No. I. JANUARY, 1879.

ORIGINAL ARTICLES.

UNIVERSITY

CALIFORS

I. ON THE TRIPARTITE CLASSIFICATION OF THE LOWER
PALEOZOIC ROCKS.

By CHARLES LAPWORTH, F.G.S.

Y those accustomed to the hopeless confusion of the Greywacké of the earlier geologists, the publication of Murchison's grand work on the "Silurian System" was hailed with feelings of the most profound relief and satisfaction. His clear and brilliant presentation of the physical and palæontological proofs of an orderly sequence among the Palæozoic Rocks below the Old Red Sandstone, as originally set forth in all their force and harmony in his magnificent volumes, naturally astonished and dazzled the majority of his scientific contemporaries, and secured for his nomenclature of these ancient deposits an almost universal acceptance. His subsequent abuse of this advantage to strengthen and consolidate his own system at the expense of that of his equally-illustrious co-workerthe less fortunate but more cautious Sedgwick-was a gallant but unscrupulous defence of this original nomenclature, which by that time he must have felt himself almost powerless to disturb. His later extension downward of the limits of his System, till it embraced all the rocks between the supposed Azoics and the Old Red Sandstone-though, in a measure, forced upon him from without— ought perhaps to be regarded in part as a very natural return to the ideas of his early teachers, who had always held the practical unity of the rocks of the Transitional period. In this way, however, Murchison unwittingly destroyed many of the most beneficial results of his own labours; in a sense, spending his old age in the attempted re-erection of the very edifice it had been the pride of his manhood to destroy-the early years of his scientific career being devoted to the worthy task of proving the marvellous variety of the Lower Palæozoics; his later years to demonstrating their integrity, unity, and indivisibility.

At the present day it would be wholly superfluous to enter upon the discussion of the vexed question of the respective claims of Sedgwick and Murchison to the Middle and Lowest Divisions of the Lower Palæozoic Rocks. We may, however, without fear of contradiction, concede to Sedgwick the credit of having been the first to

DECADE II.-VOL. VI.-NO. I.

1

determine the limits and sequence of their larger subdivisions, and to Murchison and his followers the honour of having been the first to assign them their distinctive fossils. Sedgwick worked out singlehanded the true stratigraphical arrangement of the rocks of the Lower Paleozoics of Wales, from the Bangor Beds to the summit of the Bala Series, and divided them into several successive groups, the propriety and convenience of which subsequent research has served only to make more distinctly apparent. The unavoidable-but none the less vital-defect in his earlier work lay in his not publishing the characteristic fossils of these subdivisions, until after the appearance of the great work of his rival, in which the most conspicuous forms appear as characteristic of the subdivisions of a supposed overlying system. Murchison's work, on the other hand, depended not only upon mineralogical characters and sequence of formations, but also upon palæontological peculiarities. He failed signally, however, in strictly and correctly defining his lower groups, and in correlating some of his most typical beds, with the result of greatly confusing his lists of characteristic fossils.

The rigid conservatism of Murchison in his old age, and his systematic disregard of the facts and arguments adduced in support of the Cambrian System, brought about its inevitable re-action after his death. The campaign against the Murchisonian nomenclature, so brilliantly opened by Professor Sterry Hunt, in his masterly paper on the "History of the Names Cambrian and Silurian in Geology," has since assumed extraordinary proportions. The Cambridge School, headed by Professor Hughes, the present talented occupant of the Woodwardian Chair, supported by several earnest and industrious adherents, has revived the claims of Sedgwick in all their entirety; and presses them on the attention of geologists with an energy and persistence that threatens to lead to the formation of a body of workers, determined to force from posterity, in honour of the memory of Sedgwick, the rights he demanded, but of which during his lifetime he was so unfairly deprived.

But, on the other hand, the Murchisonian nomenclature is embodied in the maps and publications of the National Survey. It is embalmed in the classic memoirs of the illustrious Barrande, and in the numerous works of the best-known geologists of Europe and America. It is still held, almost in its widest sense, by the more influential officers of the Geological Survey, and is taught to their students and subordinates with that complacent pride which has naturally been engendered by a quarter of a century of uninterrupted success. Even yet, its advocates have such an unfaltering faith in its intrinsic propriety and consequent impregnability, that the fact of the daily increasing number and ability of their opponents is either contemptuously ignored, or, at most, is deemed unworthy of a more respectful recognition than a passing smile.

The utter impossibility of reconciling the antagonistic claims of these opposing schools has led, of late years, to the formation of a third party, in which the best-known names are those of the late Sir Charles Lyell, and of Dr. Henry Hicks. These concede the

light of Murchison to all the strata between the base of the Arenig and the summit of the Ludlow, but emphatically assign the Lingula Flags and Paradoxides Beds to the Cambrian. This school-if school it may be called-has been greatly aided by the wide publicity given to their views in the numerous memoirs in which they record their steady and cautious advance in working out the natural succession among the subordinate members of the Lower Paleozoic Rocks. It is just possible that, owing to the modesty of the claims it makes for Sedgwick, and to its retention of such a large proportion of the prevalent nomenclature, this view might gradually and insensibly have taken possession of much of the field, were it not for the persistent exertions of the Cambridge School, smarting under a sense of injustice, and determined to rest satisfied with nothing less than a complete redress of those historic grievances, which their affection for the honoured name of Sedgwick has led them to regard as little less than personal to themselves.

But the partial success that has already attended the earnest conscientiousness and perseverance of the members of the Sedgwickian party has, in truth, hastened the evil day. The result that their efforts have had in calling the attention of geologists to the salient points of the question at issue, is as fatal in its effects upon their own theory, as it is upon that of their opponents. By their recent adoption of the Lyell-Hicks line of demarcation at the base of the Lower Llandovery, they furnish, indeed, a thorough demonstration of the almost perfect palæontological distinctness of the faunas of the so-called Lower Silurian formations, and those of the true or Upper Silurian, and the consequent impossibility of combining them philosophically in one and the same system. But, in spite of all that is implied to the contrary, this course is, in effect, a distinct abandonment of Sedgwick's fundamental argument that these systems were necessarily distinct, from the fact that in the typical areas their beds were stratigraphically discordant. It amounts, on the other hand, to an implicit adoption of the only safe principle, that we have no reliable chronological scale in geology but such as is afforded by the relative magnitude of zoological change-in other words, that the geological duration and importance of any system is in strict proportion to the comparative magnitude and distinctness of its collective fauna. It appears to me that it is impossible for them to rest here, but that their next and inevitable step will be the further admission that the Lyell-Hicks division of Cambrian and Lower Silurian are as rightly entitled to the rank of separate systems as the true or Upper Silurian itself; and that, eventually, their rigid sense of fairness and justice will lead them so to discriminate them.

For, amid all the confusion incident to this controversy, one grand fact stands out clear and patent to the most superficial student of Palæozoic geology - namely:- the strata included between the horizon marking the advent of Paradoxides, and the provisional line presently drawn at the summit of the Ludlow, imbed three distinct faunas, as broadly marked in their characteristic features as any of those typical of the accepted systems of a later age.

The necessity for a tripartite grouping of the Lower Palæozoic Rocks and Fossils, in partial accordance with this fact, has been very generally acknowledged for the last thirty years. The keeneyed and philosophic Barrande was the first to recognize this truth, and his addition of the "Primordial" to the First and Second Faunas of Murchison's original Silurian marked a geologic era equal in importance to the establishment of a new system. How keenly its enthusiastic discoverer watched over, and how zealously he promoted and encouraged, the gradual detection and elimination of his "Primordial" Fauna in Europe and America, are matters familiar and delightful to all earnest students of the history of discovery among the Lower Palæozoic Rocks. How the facts obtained by Phillips, Salter, and Hicks in Britain, forced even Murchison himself to adopt Barrande's views, and in his later years to become their keenest and most unsparing advocate, is equally well known. The subsequent development of the "Primordial" Fauna in Britain by Hicks, Salter, Belt, and others; in Sweden by Angelin, Nathorst Linnarsson, and Sjögren; and in America by Billings, Emmons, Hall, and Hartt, has progressed with marvellous rapidity. Every systematic geologist worthy of the name has, in his turn, been compelled to acknowledge the distinctness and first-rate importance of the "Primordial" Fauna.

Under one form or another, also, the difference in the facies of the more recent First and Second Faunas of Murchison has been universally admitted from the first, and the rock-groups formed by their including strata have been separated-at least as distinct subsystems-in all parts of the world. It is indeed true that there have been, perhaps, as many diverse views held with respect to the proper position of the line of demarcation between them, as there have been separate areas of investigation; and it is only of late that geologists have reached something like a concensus of opinion in drawing it with Hicks at the base of the Lower Llandovery. Nevertheless, no honest investigator, either British or foreign, has ever dreamt of disputing the grand fact of the distinctness of these two faunas and the consequent need for the separation of their containing rockgroups in any natural and workable plan of classification.

Thus, it is hardly possible that any geologist, who is familiar with the rocks and fossils of the Lower Palæozoics, or who is even fairly versed in the literature of the subject, would at present venture to deny the proposition that between the base of the known fossiliferous series and that of the Old Red Sandstone there lie three successive rock-groups-each of which is characterized by a special fauna of first-rate geologic importance.

Further insistence upon this point is probably needless. But if the fact be once admitted, it follows of necessity that the interests of science demand that these three successive rock-systems shall be distinguished by three separate and unmistakable titles.

At this stage, however, we plunge into the very midst of the conflict of the schools. Friends, foes, and spectators, seem all fairly agreed as to the advisability of a triple division of the sediments.

The points around which the strife is at its keenest bear upon the question as to whether these three divisions are of equal classificatory value, and if so, which party has the best right to give them their

names.

The strict Murchisonian of the present day claims for the Silurian all the fossiliferous strata that lie between the Archean and the Devonian, and arranges them in his three sub-systems of the Primordial, Lower, and Upper Silurian. If he is a palæontologist, he seizes at once upon the indisputable fact that the general facies of the fossils of these three divisions, when viewed in their collective aspect, has a marked character of its own, wholly distinct from that of the faunas of the overlying rock-groups. Profoundly impressed by this distinction, the less striking differences between the faunas of the three members of the Lower Palæozoic itself dwindle in his eyes into utter insignificance, and the slightest party bias is sufficient to lead him to regard them with Barrande as forming "one grand and indivisible triad which is the Silurian System.' As discovery progresses, gradually demonstrating the former presence of organic existences in strata far below the base-line laid down by the founder of his system, departing gradually in facies from his typical fauna (but, nevertheless, connected therewith by almost imperceptible gradations), his former admission, and the traditions of his school, compel him to keep pace with it, extending his system and fauna downwards step by step. The result is, that if he is consistent, he is at last driven to demand also, with Barrande, the inclusion of the beds which Murchison, even in his latest years, acknowledged to be the very basement rocks of a pre-Silurian system.

If, on the other hand, he is a stratigraphist, he instances the fact that in Britain and America no general stratigraphical discordance interrupts the vertical succession of formations between the Archean and the Carboniferous. He points to the Llandovery beds of Britain, and shows that the grandest stratigraphical break in the entire series in the typical area occurs in the heart of a group of beds that the founder of his school placed partly in one sub-system and partly in the other; but which he, in common with all scrupulous geologists, included in a single formation, whose essential unity he fearlessly challenges his opponents to deny. He calls attention to the Colonies of Bohemia to show that even where the paleontological distinction between the sub-systems is most abrupt, yet, according to the greatest of Silurian palæontologists, there is actually an alternation of the two faunas in the beds of passage. Or, he points triumphantly to the succession in Scandinavia, where the Lower Palæozoics are reduced to a collective thickness of a few hundreds of feet, and are occasionally folded up and entangled almost inextricably together in a single section, and asks how is it possible to doubt the unity of a System whose members are individually of such insignificant dimensions, and, physically, are so indissolubly united!

The moving principle of the Sedgwickian, on the contrary, is the demand for historic justice. With true British instinct, he recognizes