ARTICLE VII-Correspondence of JOACHIM BARBANDE, SIR WILLIAM LOGAN and JAMES HALL, on the Taconic System and on the age of the Fossils found in the Rocks of Northern New England, and the Quebec Group of Rocks.

(From the American Journal of Science No. 92, 1861.)

I. INTRODUCTORY REMARKS.

As some of our foreign readers may not be acquainted with the question to which the following important correspondence relates, we think it advisable to make a few explanatory observations by way of introduction. A complete history of the whole subject would require a greater amount of space than can be afforded, and we shall therefore touch only upon a few of the more salient points.

The rocks under discussion occupy a belt of country east and west from twenty to sixty miles wide, stretching from the vicinity of the city of New York in a northerly direction to Lake Champlain and thence through Vermont and Lower Canada to Cape Gaspé at the mouth of the St. Lawrence. The strata, consisting of slates, limestones, sandstones and conglomerates are greatly disturbed, plicated and dislocated, and are often, especially along the eastern side of the belt, in a highly metamorphic condition. On this side they are overlaid unconformably by Upper Silurian and Devonian rocks, but on the western and northern margin they are in contact with and in general seem to be a continuation of the Lower Silurian. Some of the slates of the formation closely resemble in lithological characters those of the Hudson River group, and thus along the western side of the region, where the junction of the two formations occurs, it is often almost impossible to draw the line between them. The dip and strike of both are in the same direction, and throughout extensive areas the newer rocks appear to plunge beneath the older. The whole district affords an excellent example of those cases, so well known to field geologists, where the true relations of the different masses cannot be clearly worked out without the aid of fossils, and where the best observers may arrive at diametrically opposite opinions.

Dr. Emmons, one of the geologists of the New York Survey, early convinced himself by a careful examination of these rocks, that they constituted a distinct physical group more ancient than the Potsdam sandstone, the latter being regarded by him as the base of the Lower Silurian System in North America. His

views were given in detail in 1842 in his final report on that part of the State confided to his charge, and in a more special manner in another work entitled "THE TACONIC SYSTEM," published in 1844. In this latter work he figured several species of fossils which had been collected in different parts of the formation. Two of these were trilobites, and were described under the names of Atops trilineatus and Elliptocephala asaphoides. The others were graptolites, fucoids and apparently trails of annelides; he considered all the species to be distinct from any that had been found in American rocks of undoubted Silurian age. The pre-silurian age of the formation has also been maintained by him in several more recent publications such as his "American Geology"-the several reports on the geological survey of North Carolina and in his "Manual of Geology."

On the other hand, Professor Hall placed the whole region in the Hudson River group. In the first volume of the Paleontology of New York he identifies Atops trilineatus with Triarthrus Beckii, the characteristic trilobite of the Utica slate;-Elliptocephala asaphoides he refers to the genus Olenus, and describes as congeneric therewith, another trilobite (O. undulostriatus) said to be from the true Hudson River shales. It is scarcely necessary to state that these identifications have always afforded an extremely powerful objection against the correctness of the position assumed by Emmons, because no species of trilobite is known to range from the Primordial zone up to the top of the Lower Silurian. Hall's first volume was published in 1847 and as it is unquestionably the most important work on the Lower Silurian fossils of North America it has been very generally accepted by our physical geologists as a guide. It is not surprising therefore, that in all the discussions that have taken place during the last fourteen years upon the age of these rocks, the majority of those who did not profess to be naturalists should have arranged themselves on the side of the leading paleontologist of the country.

The formation was traced from New York through Vermont, and there identified by Prof. Adams, the State Geologist, with the Hudson River group. The Canadian Surveyors continued it with great labor through a mountainous and partially uninhabited country for nearly five hundred miles further, from the northern extremity of Vermont to the neighborhood of Quebec, and thence along the south side of the St. Lawrence to the mouth

of that river at Cape Gaspé. In Canada the nomenclature of the New York Survey was adopted for all the formations, and it appears from his several reports that Sir W. E. Logan could find nothing in the physical structure of the country to authorize him to make an exception in favor of this particular series of rocks. It has therefore always been called the Hudson River group in the publications of the Canadian Survey.

It will be seen by the following correspondence that the new light thrown upon the question of the age of these rocks by the fortunate discovery of a large number of fossils near Quebec, now leads Sir William to place them at the base of the Lower Silurian, and as he states that the shales in Vermont, in which the trilobites noticed in Mr. Barrande's letter to Prof. Bronn have been found, may be subordinate to the Potsdam, it seems probable that the sequence contended for by Emmons will turn out to be at least for the greater part the true one.

II.

ON THE PRIMORDIAL FAUNA AND THE TACONIC SYSTEM OF EMMONS, IN A LETTER TO PROF. BRONN OF HEIDELBERG.*

"PARIS, July 16, 1860.

"........ I have recently received, thanks to the kindness of Mr. E. Billings, the learned paleontologist of the Geological Survey of Canada, a very interesting pamphlet entitled 'Twelfth Annual Report of the Regents of the University of the State of New York, 1859.' If you possess this publication, you will find there, at page 59, a memoir of Prof. J. Hall, entitled 'Trilobites of the shales of the Hudson River group.' This savant there describes three species under the names Olenus Thompsoni, Olenus Vermontana, and Peltura (Olenus) holopyga. The well-defined characters of these trilobites are described with the clearness and precision to be expected from so skilful and experienced a palæontologist as James Hall.

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Although the specimens are incomplete, their primordial nature cannot admit of the least doubt, when the descriptions are read, accompanied with wood engravings, which the large dimensions of these three species render sufficiently exact. The first is 105 millim. long by 80 broad, the other two are somewhat smaller.

• Proceed. Boston S. N. Hist., Vol. vii, Dec. 1860, p. 371.

"The heads of the two Oleni being injured, the furrows of the glabella cannot be recognized. The thorax has a common and remarkable character, which consists in the greater development of the third segment, the point of which is stronger and longer than in all the other pleura. This is a striking resemblance to the Paradoxides, the second segment of which has the same peculiarity. Besides, there is an intimate relation between these two primordial types, and we should not be surprised if America furnished us with forms uniting most of their characteristics. The pygidium of O. Thompsoni, the only one that is known, shows no segmentation, and attests by its exiguity its relation to a primordial trilobite. P. holopyga, by its whole appearance, resembles the Swedish species so well known by the name of P. scarabæoides.

"Thus all the characters of these three trilobites, as they are recognized and described by J. Hall, are those of the trilobites of the primordial fauna of Europe. This is so true, that I think I may say without fear, if M. Angelin, or any other palæontologist practised in distinguishing the trilobites of Scandinavia, had met with these three American forms in Sweden or Norway, he would not have hesitated to class them among the species of the primordial fauna, and to place the schists enclosing them in one of the formations containing this fauna. Such is my profound conviction, and I think any one who has made a serious study of the trilobitic forms and of their vertical distribution in the oldest formations will be of the same opinion.

"Besides, all who have seriously studied palæontology know well that each geological epoch, or each fauna, has its proper and characteristic forms, which once extinct reappear no more. This is one of the great and beautiful results of your immense researches, which have generalized this law, recognized by each one of us within the limits of the strata he describes.

"The great American palæontologist arrived long since at the same conclusion, for in 1847 he wrote the following passage in the Introduction to the first volume of the monumental work consecrated to the Paleontology of New York.

"Every step in this research tends to convince us that the succession of strata, when clearly shown, furnishes conclusive proofs of the existence of a regular sequence among the earlier organisms. We are more and more able, as we advance, to observe that the Author of nature, though always working upon

the same plan and producing an infinite variety of forms almost incomprehensible to us, has never repeated the same forms in successive creations. The various organisms called into existence have performed their parts in the economy of creation, have lived their period and perished. This we find to be as true among the simple and less conspicuous forms of the paleozoic series, as in the more remarkable fauna of later periods.'-J. Hall, Pal. of New York,' i. p. xxiii."

“When an eminent man expresses such ideas so eloquently, it is because they rise from his deepest convictions. It must then be conceived that Mr. Hall, restrained by the artificial combinations of stratigraphy previously adopted by him, has done violence to his paleontological doctrines, when, seeing before him the most characteristic forms of the Primordial fauna, and giving them names the most significant of this first creation, he thinks it his duty to teach us that these three trilobites belong to a horizon superior to that on which the second fauna is extinguished.

"In effect, according to the text of Mr. Hall, the three trilobites in question were found near the town of Georgia, Vermont, in schists which are superior to the true Hudson River group. In his works Mr. Hall does not go beyond indicating the horizon of certain fossils, and no one would think of asking from him a guaranty for such indications. But on this occasion the great American palæontologist thinks it necessary to support his stratigraphical determination by another authority, chosen from the most respectable names in geology. The following is the note which terminates his Memoir.

"NOTE.-In addition to the evidence heretofore possessed regarding the position of the shales containing the Trilobites, I have the testimony of Sir W. E. Logan, that the shales of this locality are in the upper part of the Hudson River group, or forming a part of a series of strata which he is inclined to rank as a distinct group, above the Hudson River proper. It would be quite superfluous for me to add one word in support of the opinion of the most able stratigraphical geologist of the American continent.'

"Now, when a savant like Mr. Hall thinks himself obliged to invoke testimony to guarantee the exactness of the position of certain fossils, it is clear that the determination of this position presents some difficulties.

"In order to understand these difficulties I have consulted the