The Trilobite is supposed by many naturalists to be one of the first animated beings of our earth called into existence by the great Author of nature.[3] It was first noticed more than two centuries ago, among the petrifactions which abound in a calcareous rock, at Dudley, in England, and was from this circumstance, called for a long time, the Dudley fossil. Linné gave it the name of the Paradoxical insect; but whether an insect, a crustaceous animal, or a shell, is still considered by many as problematical.
[3] It is obvious, that if most of the gelatinous animals which now inhabit our seas, were to become extinct, few or no traces of them could be found in any succeeding depositions of earthy matter. Whatever kind of animal life, therefore, may have been the first which appeared in our planet, must be entirely hypothetical. All that we can with certainty say of it, is, that it was best adapted to the circumstances, in which it was to exist, and that it was consistent with the wisdom and design which we see every where pervading the universe.
Notwithstanding the high antiquity of the family of the Trilobites, and the remarkable characters the different individuals which compose it, sustain in the animal kingdom; till within a very few years, the whole race has been almost entirely neglected by naturalists. The first attempt at any systematic arrangement of the genera and species, was made in 1815, by Alexander Brongniart, Professor of Mineralogy, &c. &c., in Paris.[4] Until that period, the term Entomolithus Paradoxus, proposed by Linné, was applied to all the fossil remains, which in their general appearance bore any resemblance to that found at Dudley, and which he first described under that name. The confusion, therefore, which existed in this department of natural science, may readily be imagined; especially, as the species rapidly multiplied, when they were supposed to throw some rays of light on certain obscure geological phenomena. Soon after the appearance of Professor Brongniart's excellent work, the attention of other naturalists was directed to this neglected part of creation. The most important memoir, on account of the number of species, well figured and described in it, is one by Dr. E. W. Dalmann, published in the Transactions of the Swedish Academy, for 1826. There is also in the Acts of the Royal Society, at Upsal, an excellent paper on this subject by Professor Wahlenberg. Our highly esteemed friend, Dr. James E. Dekay, has also given in the first volume of the Annals of the Lyceum of Natural History of New York, some very interesting and ingenious observations on the nature and the structure of the Trilobites, with a description of a new genus. These are the principal authorities which have been consulted in arranging the present work.
[4] I cannot let this opportunity pass, without acknowledging my obligations to Professor Brongniart, for his civilities, when on a late visit to Paris. Every one whose curiosity leads him to examine the royal manufactory of porcelain, at Sevres, of which he is the director, will no doubt acknowledge that his talents as a philosopher, are rivalled by his accomplishments as a gentleman.
Our object in the present undertaking being merely to give a monograph of the species of Trilobites found in the rocks of North America; we leave to other and abler hands the more difficult and interesting task of determining with precision the connexion which may exist between these organic reliques, and the relative ages of the strata in which they are found.
It is supposed, indeed, that a sufficient number of well characterized species have not yet been collected and accurately described, to throw any certain and clear light on otherwise doubtful geological phenomena. What has been remarked by De Candolle, with regard to botanical geography, is perhaps true of these fossils as to solving the difficult problems of geology—"Let us not forget," says he, "that this science can only be commenced when the study of species has been sufficiently advanced to furnish us with numerous and well authenticated facts."
We are well aware of the difficulty of settling the line which ought to divide species. Individuals perfectly identical in all their parts, are rarely, if ever seen; though a general resemblance may be easily traced. Among fossils, just discriminations of this kind are more delicate, than in recent specimens. The hand of time, accidental causes, and the influence of atmospheric changes often produce such characters as to render the determination of fossil species an exceedingly difficult task. We have no doubt, therefore, that a few of our Trilobites, which are now considered as perfectly identical with some found in Europe, will upon fuller examination, be discovered to be dissimilar, and of course certain geological speculations grounded on the first opinion, be ultimately abandoned.
The geographical distribution of organic remains, is an exceedingly curious inquiry. If accurately pursued, without reference to any preconceived theory, it will no doubt furnish much information as to the comparative ages of the different strata which compose the external crust of our planet—for that these strata were deposited or formed at periods of time more or less remote from each other, every one knows, to be a generally admitted geological fact. The occurrence of similar fossils in districts of country remotely situated from each other, certainly presents a phenomenon highly interesting to the speculative naturalist, and apparently indicates that the same powerful and general causes must have concurred to produce these isomorphous depositions. No fossils have contributed more to this kind of information, than those of shells, and as the mineralized species could not be satisfactorily studied, except by accurately comparing them with those which now inhabit our seas and continents; the search for shells, has become, from a simple amusement, the study of scientific men—or, as a writer remarks, "it was only after the period when it was perceived that geology and ancient zoology were destined to be enlightened by their fossil remains, that this research passed from the hands of amateurs into those of naturalists."[5]
[5] We have not unfrequently noticed, both in the writings and conversation of some geologists, a disposition to sneer at the subsidiary branches of natural history. Mineralogy and conchology, are light and mean in their estimation, when compared with the study of extensive strata and ponderous boulders. Like Irving's testy governor of Manahatta, who settled the accounts of his clients by placing their books in the opposite scales of a balance, they decide on the value of a science, by the absolute weight of the objects embraced by it. Geology, as well as any other branch of natural history, may degenerate into a mere love for the curious, or have for its principal aim, the perfection or improvement of some ideal system of classification, without advancing a single step further.
Another curious geological fact appears to be established more especially by fossil trilobites; it is that precisely the same species of animal relic, is the most generally diffused over the globe, in proportion to the antiquity of the rock which contains it. Thus the transition limestone of England, France, Germany and Sweden, contains the species called the Calymene of Blumenbach, in common with the same formation which extends over so large a portion of the United States.