A century of science in America

by Unknown

Dana in his review of the Silurian-Cambrian controversy states: “The claim of a worker to affix a name to a series of rocks first studied and defined by him cannot be disputed.” We have seen that Murchison had priority of publication in his term Silurian over Sedgwick’s Cambrian, but that in a complete presentation, both stratigraphically and faunally, the former had years of prior definition. What has even more weight is that geologists nearly everywhere had accepted Murchison’s Silurian system as founded upon the Lower and Upper Silurian formations. A nomenclature once widely accepted is almost impossible to dislodge. However, in regard to the controversy it should not be forgotten that it was only Murchison’s Lower Silurian that was in conflict with Sedgwick’s Upper Cambrian. As for the rest of the Cambrian, that was not involved in the controversy.

Dana goes on to state that science may accept a name, or not, according as it is, or is not, needed. In the progress of geology, he thought that the time had finally been reached when the name Cambrian was a necessity, and he included both Cambrian and Silurian in the geological record. The “Silurian,” however, included the Lower and Upper Silurian—not one system of rocks, but two.

It is now twenty-seven years since Dana came to this conclusion, at a time when it was believed that there was more or less continuous deposition not only between the formations of a system but between the systems themselves as well. To-day many geologists hold that in the course of time the oceans pulsate back and forth over the continents, and accordingly that the sequence of marine sedimentation in most places must be much broken, and to-day we know that the breaks or land intervals in the marine record are most marked between the eras, and shorter between all or at least most of the periods. Furthermore, in North America, we have learned that the breaks between the systems are most marked in the interior of the continent and less so on or toward its margins.

Hardly any one now questions the fact of a long land interval between the Lower Silurian and Upper Silurian in England, and it is to Sedgwick’s credit that he was the first to point out this fact and also the presence of an unconformity. It therefore follows that we cannot continue to use Silurian system in the sense proposed by Murchison, since it includes two distinct systems or periods. Dana, in the last edition of his Manual of Geology (1895), also recognizes two systems, but curiously he saw nothing incongruous in calling them “Lower Silurian era” and “Upper Silurian era.” It certainly is not conducive to clear thinking, however, to refer to two systems by the one name of Silurian and to speak of them individually as Lower and Upper Silurian, thus giving the impression that the two systems are but parts of one—the Silurian. Each one of the parts has its independent faunal and physical characters.

We must digress a little here and note the work of Joachim Barrande (1799–1883) in Bohemia. In 1846 he published a short account of the “Silurian system” of Bohemia, dividing it into étages lettered C to H. Between 1852 and 1883 he issued his “Système Silurien du Centre de la Bohème,” in eighteen quarto volumes with 5568 pages of text and 798 plates of fossils—a monumental work unrivalled in paleontology. In the first volume the geology of Bohemia is set forth, and here we see that étages A and B are Azoic or pre-Cambrian, and C to H make up his Silurian system. Etage C has his “Primordial fauna,” now known to be of Paradoxides or Middle Cambrian time, while D is Lower Silurian, E is Upper Silurian, F is Lower Devonian, and G and H are Middle Devonian. From this it appears that Barrande’s Silurian system is far more extensive than that of Murchison, embracing twice as many periods as that of England and Wales.

About 1879 there was in England a nearly general agreement that Cambrian should embrace Barrande’s Primordial or Paradoxides faunas, and in the North Wales area be continued up to the top of the Tremadoc slates. To-day we would include Middle and Upper Cambrian. Lower Cambrian in the sense of containing the Olenellus faunas was then unknown in Great Britain.

Lapworth, recognizing the distinctness of the Lower Silurian as a system, proposed in 1879 to recognize it as such, and named it Ordovician, restricting Silurian to Murchison’s Upper Silurian. This term has not been widely used either in Great Britain or on the Continent, but in the last twenty years has been accepted more and more widely in America. Even here, however, it is in direct conflict with the term Champlain, proposed by the New York State Geologist in 1842.

In 1897 the International Geological Congress published E. Renevier’s Chronographie Géologique, wherein we find the following:

Silurian Period.	Upper or Silurian (Murchison, restricted, 1835).	Ludlowian (Murchison 1839).
		Wenlockian (Murchison 1839).
		Landoverian (Murchison).
	Middle or Ordovician (Lapworth 1879).	Caradocian (Murchison 1839).
		Landeilian (Murchison 1839).
		Arenigian (Sedgwick 1847).
	Lower or Cambrian (Sedgwick, restricted, 1835).	Potsdamian (Emmons 1838).
		Menevian (Salter and Hicks 1865).
		Georgian (Hitchcock 1861).

Regarding this period, which, by the way, is not very unlike that of Barrande, Renevier remarks that it is “as important as the Cretaceous or the Jurassic. Lapworth even gives it a value of the first order equal to the Protozoic era.”