By Nomenclature we mean a system of names; and hence we can [528] not speak of a Geological Nomenclature till we come to Werner and Smith. The earlier mineralogists had employed names, often artificial and arbitrary, for special minerals, but no technical and constant names for strata. The elements of Werner’s names for the members of his geological series were words in use among miners, as Gneiss, Grauwacke, Thonschiefer, Rothe todte liegende, Zechstein; or arbitrary names of the mineralogists, as Syenite, Serpentine, Porphyry, Granite. But the more technical part of his phraseology was taken from that which is the worst kind of name, arbitrary numeration. Thus he had his first sandstone formation, second sandstone, third sandstone; first flötz limestone, second flötz limestone, third flötz limestone. Such names are, beyond all others, liable to mistake in their application, and likely to be expelled by the progress of knowledge; and accordingly, though the Wernerian names for rocks mineralogically distinguished, have still some currency, his sandstones and limestones, after creating endless confusion while his authority had any sway, have utterly disappeared from good geological works.
The nomenclature of Smith was founded upon English provincial terms of very barbarous aspect, as Cornbrash, Lias, Gault, Clunch Clay, Coral Rag. Yet these terms were widely diffused when his classification was generally accepted; they kept their place, precisely because they had no systematic signification; and many of them are at present part of the geological language of the whole civilized world.
Another kind of names which has been very prevalent among geologists are those borrowed from places. Thus the Wernerians spoke of Alpine Limestone and Jura Limestone; the English, of Kimmeridge Clay and Oxford Clay, Purbeck Marble, and Portland Rock. These names, referring to the stratum of a known locality as a type, were good, as far as an identity with that type had been traced; but when this had been incompletely done, they were liable to great ambiguity. If the Alps or the Jura contain several formations of limestone, such terms as we have noticed, borrowed from those mountains, cease to be necessarily definite, and may give rise to much confusion.
Descriptive names, although they might be supposed to be the best, have, in fact, rarely been fortunate. The reason of this is obvious;—the mark which has been selected for description may easily fail to be essential; and the obvious connexions of natural facts may overleap the arbitrary definition. As we have already stated in the history of botany, the establishment of descriptive marks of real classes presupposes the important but difficult step, of the discovery of such marks. [529] Hence those descriptive names only have been really useful in geology which had been used without any scrupulous regard to the appropriateness of the description. The Green Sand may be white, brown, or red; the Mountain Limestone may occur only in valleys; the Oolite may have no roe-like structure; and yet these may be excellent geological names, if they be applied to formations geologically identical with those which the phrases originally designated. The signification may assist the memory, but must not be allowed to subjugate the faculty of natural classification.
The terms which have been formed by geologists in recent times have been drawn from sources similar to those of the older ones, and will have their fortune determined by the same conditions. Thus Mr. Lyell has given to the divisions of the tertiary strata the appellations Pleiocene, Meiocene, Eocene, accordingly as they contain a majority of recent species of shells, a minority of such species, or a small proportion of living species, which may be looked upon as indicating the dawn of the existing state of the animate creation. But in this case, he wisely treats his distinctions, not as definitions, but as the marks of natural groups. “The plurality of species indicated by the name pleiocene must not,” he says,[49] “be understood to imply an absolute majority of recent fossil shells in all cases, but a comparative preponderance wherever the pleiocene are contrasted with strata of the period immediately preceding.”
[49] Geol. iii. 392.
Mr. Lyell might have added, that no precise percentage of recent species, nor any numerical criterion whatever, can be allowed to overbear the closer natural relations of strata, proved by evidence of a superior kind, if such can be found. And this would be the proper answer to the objection made by De la Beche to these names; namely, that it may happen that the meiocene rocks of one country may be of the same date as the pleiocene of another; the same formation having in one place a majority, in another a minority, of existing species. We are not to run into this incongruity, for we are not so to apply the names. The formation which has been called pleiocene, must continue to be so called, even where the majority of recent species fails; and all rocks that agree with that in date, without further reference to the numerical relations of their fossils, must also share in the name.
To invent good names for these large divisions of the series of strata is indeed extremely difficult. The term Oolite is an instance in which [530] a descriptive word has become permanent in a case of this kind; and, in imitation of it, Pœcilite (from ποικίλος, various,) has been proposed by Mr. Conybeare[50] as a name for the group of strata inferior to the oolites, of which the Variegated Sandstone (Bunter Sandstein, Grès Bigarré,) is a conspicuous member. For the series of formations which lies immediately over the rocks in which no organic remains are found, the term Transition was long used, but with extreme ambiguity and vagueness. When this series, or rather the upper part of it, was well examined in South Wales, where it consists of many well-marked members, and may be probably taken as a type for a large portion of the rest of the world, it became necessary to give to the group thus explored a name not necessarily leading to assumption or controversy. Mr. Murchison selected the term Silurian, borrowed from the former inhabitants of the country in which his types were found; and this is a term excellent in many respects; but one which will probably not quite supersede “Transition,” because, in other places, transition rocks occur which correspond to none of the members of the Silurian region.
[50] Report, p. 379.
Though new names are inevitable accompaniments of new views of classification, and though, therefore, the geological discoverer must be allowed a right to coin them, this is a privilege which, for the sake of his own credit, and the circulation of his tokens, he must exercise with great temperance and judgment. M. Brongniart may be taken as an example of the neglect of this caution. Acting upon the principle, in itself a sound one, that inconveniences arise from geological terms which have a mineralogical signification, he has given an entirely new list of names of the members of the geological series. Thus the primitive unstratified rocks are terrains agalysiens; the transition semi-compact are hemilysiens; the sedimentary strata are yzemiens; the diluvial deposits are clysmiens; and these divisions are subdivided by designations equally novel; thus of the “terrains yzemiens,” members are—the terrains clastiques, tritoniens, protéïques, palæotheriens, epilymniques, thalassiques.[51] Such a nomenclature appears to labor under great inconveniences, since the terms are descriptive in their derivation, yet are not generally intelligible, and refer to theoretical views yet have not the recommendation of systematic connexion.