looked by later writers. Who does not see what amount of error may accrue from the indiscriminate use of materials which are not first submitted to a very critical revision in these different respects, not to speak of the general difficulty of agreeing upon the limits of specific differences. With regard to this last point, however, I would say that whosoever would only use in discussing general questions materials revised candidly with the same principles, could not fail to obtain at least uniform results. And when the results of investigations made upon materials corrected in different ways by different authors are compared with one another, if these differences are kept in view, the disagreement in the results would not be found so great as it might otherwise The astronomers and physicists have long learned to correct their observations before using them, and to take into consideration what they call the personal equation of different observers; are we never to learn from them a lesson in the estimation of our respective investigations, and shall our facts for ever be used without being first corrected for all the possible causes of error and disagreement? As long as there are differences of opinion respecting the natural limits of genera and species, is it not absolutely necessary to reduce or expand the scale applied to the investigations of different authors, when using them for the same purposes, exactly in the same manner as thermometric observations made with the scales of Reaumur or Celsius or Fahrenheit are reduced to the same standard, before being compared.

seem.

In the second place, species must be referred to genera circumscribed within the same limits, before they can fairly be compared or at least lead to trustworthy general results. As long as certain bivalve shells of the carboniferous and oolitic series were referred to the genus Unio, it could appear that the family of Naiades began its existence at a very early period; but since the oolitic species of this kind have been ascertained to differ essentially from our freshwater shells, and to constitute by themseles a natural genus more closely allied to Crassatella than to Unio, nobody thinks any longer of looking for Unios in marine deposits. As long as certain fossil fishes of the Zechstein and Lias were referred to the genera Esox and Cyprinus, the families of which these genera are the types could be supposed to have extended their range far beyond the tertiary formations, before which however no one of their representatives is to be found. Before the Spatangoids were divided into natural genera, the genus Spatangus was mentioned among the fossils of the oolitic as well as the cretaceous and tertiary formations; now it is restricted to the last among the fossils and found also among the living. I do not believe that a single genuine species of Gorgonia is found among the fossil Polypi, and yet that genus appears in the lists of fossils from the paleozoic period to the present time.

Since it is not my intention to enter here upon a special criticism of the innumerable errors of this kind, still to be found in even modern lists of fossils, I shall not multiply my examples. These may be sufficient to show how importaut a correct generic identification of the fossils may be in the estimation of the order of succession of organized beings; and I cannot but lament the utter want of consideration evinced even by many distinguished palæontologists in this respect, who seem to think that the knowledge of species is sufficient in itself to a proper appreciation of the order of creation, and that genera are arbitrary divisions established by naturalists merely for the sake of facilitating the study of species, as if the more general relations of living beings to one another were not as definitely regulated in all their degrees by the same thinking mind, as the ultimate relations of individuals to one another.

In the third place the natural affinities of genera should be ascertained. Unless the genera are referred to the families to which they truly belong, unless the rank of these families in their respective classes is positively determined, unless the peculiarities of structure which characterizes them is taken as the foundation of such an arrangement and further corroborated by the mode of development of their respective types, it would be a hopeless task to attempt to determine the order of succession of the fossils in different geological formations. Before the Crinoids which Lamark placed along the Polyps had been referred to the class of Echinoderms, nobody could have understood the beautiful gradation so fully ascertained now, which may be traced through all geological formations among these animals. Before it was ascertained that the little animal described by Thompson under the name of Pentacrinus europeus, as a living Crinoid, for which De Blainville established the genus Phytoerinus, is in reality the young of a Comatula, nobody could have suspected the wonderful relations which exist between the changes animals now living undergo during their growth, and the order of succession of entire classes of animals during successive geological ages. As long as the natural position of Trilobites remained doubtful in the animal kingdom, the characters of the prototypes of the class of Crustacea could not be appreciated. Who does not see how impossible it was for those who classified the Trilobites with the Chitons to arrive at any sound results respecting the gradation and order of succession of these animals? Whilst now they are beautifully linked to the Macrura of the Trias, by the gigantic Entomostraca of the Devonian and Carboniferous periods. Again, the knowledge of the embryology of Crustacea gives us a key to a correct appreciation of the early appearance of the Macrura and the late introduction of the Brachyura. The removal of the Bryozoa from among Polypi to the class of Mollusks, will entirely

change the aspect and relations of the fauna of the paleozoic rocks. How different, again, would the order of succession of Mollusks appear, were we to adhere to Cuvier's view of separating the Brachiopods, as a class, from the other Acephala, to which they are now more correctly referred The vexed question of the period of appearance of Dicotyledonous plants in the geological series would have been settled long ago, had it been placed upon its real foundation. It is not in reality to be argued upon paleontological evidence chiefly, for it resolves itself in the main into a botanical question, and the definite answer must depend upon the position finally assigned by botanists to the families of Coniferæ and Cycadeæ. If these natural orders of plants are really allied to the Dicotyledonæ, then this type begins with the paleozoic rocks in the Devonian system, and there is no gradation in the order of succession of plants during geological times. But if the view of Brongniart is more correct, if the Coniferæ and Cycadeæ have to be separated from the Dicotyledonæ as Gymnospermæ, and if moreover these latter should prove, as I believe they are, inferior even to the Monocotyledoneæ, then we may at once recognize in the vegetable kingdom a similar gradation of types as among animals. These examples may suffice to show what is required for a proper investigation of the order of succession of organized beings in the course of time, and how little confidence the investigations in this field deserve, which have not been made with due reference to all the points mentioned above. It is indeed only in the classes, the structure and embryology of which is equally well understood, we are able to discover the laws regulating the succession of animals and plants in geological formations, and our knowledge is at present still too imperfect to carry the investigation into all families of the animal kingdom. And yet enough is known to leave no doubt as to the final result; we may confidently await the time when the glory of the wonderful order of creation shall be fully revealed to us, and this may stimulate us to renewed efforts, since the success depends entirely upon our own exertions.

The geographical distribution of animals began only to be studied long after systematic zoology had made considerable progress, but even to this day the limits of the faunæ are nowhere circumscribed with any kind of precision, the principles upon which they might be determined are in many respects questionable, and a large number of animals are daily described without any reference to their natural distribution upon the earth; though much has already been done since Buffon to place this branch of our knowledge upon a better foundation, and especially to ascertain the laws regulating the geographical distribution of certain classes and families considered isolately. The point which requires now particular attention, is the combination of these differ

pres

ent types within definite regions, and their common circumscription within natural zoological provinces. This study would be particularly important with reference to the comparison of the local fauna of former geological periods with those of the ent creation. But since the latter even are comparatively little known, we must be satisfied to wait for the time when thorough comparisons shall be possible between the local fauna of each and all geological periods inter se, and with those of other periods.

In closing this digression, I may sum up my criticism upon palæontological investigations, by saying that any generalization respecting the succession of organized beings which is not based upon materials in which the synchronism and succession of species and their geographical distribution is not duly considered, and in which the identification of species is not made with reference to sound zoological principles, with due regard to the equal limitation of genera, and also with reference to our improved classifications in zoology, is not fit to be trusted. All species taken into consideration should undergo a revision with reference to their chronology, their topography and their zoology, and in the last point of view the range and natural limitation as well as identity of the species, their generic affinities and their zoological classification should be equally tested.

Returning now to the main subject of this paper, I have further to say that the very fact that certain stratified rocks, even among the oldest formations, are almost entirely made up of fragments of organized beings, should long ago have satisfied the most skeptical that both animal and vegetable life was as active and profusely scattered upon the whole globe, at all times and during all geological periods, as it is now. No coral reef in the Pacific contains a larger amount of organic debris than some of the limestone deposits of the tertiary, of the cretaceous, or of the oolitic, nay even of the palæozoic periods, and the whole vegetable carpet covering the present surface of the globe, even if we were to consider only the most luxurious vegetation of the tropics, and leave entirely out of consideration the whole expanse of the ocean, as well as those tracks of land where under less favorable circumstances the growth of plants is more reduced, would not form one single seam of workable coal to be compared to the many thick beds contained in the rocks of the Carboniferous period alone.

ART. XXXIII.-New Localities of Meteoric Iron; by CHARLES UPHAM SHEPARD, M.D.

1. Tazewell, Claiborne county, Tennessee.

For the specimens of the highly interesting mass here described I am indebted to Prof. J. B. Mitchell, of the East Tennessee University, at Knoxville. Though but a fragment of three

ths pounds, (having been detached from a mass originally weighing sixty pounds,) it nevertheless has much the appearance of an independent meteorite. Its shape is that of an elongated three-sided pyramid, whose axis is slightly oblique, and whose upper edges are obscurely truncated, so as to resemble an imperfectly formed six-sided pyramid of corundum. The height of the mass is four inches. The base is triangular and nearly smooth, presenting however a cleavage surface, partially coated by brown oxyd of iron. By this face, it was originally connected with the larger mass, of which it doubtless formed one of the sharpest extremities. It is certainly very remarkable that the cleavage should have been effected without leaving any hackly projections, the more so as the mass itself by no means yields to a similar cleavage in any direction whatever. Possibly the cleavage was occasioned by the interposition of a seam of pyrites, in the direction in which it took place. At any rate, its occurrence shows that these lumps, though generally composed of very tough and strongly coherent materials, are nevertheless susceptible of cleavage in certain directions, and that they may occasionally explode or subdivide into numerous fragments, without the necessity of any very considerable force.

The upper planes of the pyramid are indented, and somewhat undulating, as is usual in meteoric irons; but there is no thick

* The following is an abstract from Prof. Mitchell's letter in reference to its discovery: "This meteorite was found April, 1853, about ten miles west of Tazewell, Claiborne county, Tennessee. It was discovered by a son of William Rogers, while ploughing in clayey ground on the side of a hill, where the soil had been much washed away by rains. His attention was arrested by the resistance and noise produced, when the mass was struck by the plough. The lump weighed about sixty pounds. It was very irregular in its shape. The period of its fall is of course unknown. On account of its weight and lustre, it was regarded as silver; and it was with no small difficulty that the finder was induced to part with it, even by my paying him what appeared to be an equivalent, and then agreeing to give him its weight in silver, provided it should prove to be that metal, when properly examined. For my first information of the iron, I am indebted to J. C. Ramsay, Esq., a gentleman who, not limiting his researches to the mere details of his profession, loses no opportunity of contributing to several branches of natural history. I retain a fragment of about six ounces which he first gave me for examination. The remainder of a mass was broken when I saw it into two pieces, one of which, weighing perhaps three and a half pounds, I send to you. The largest portion, I transferred as I informed you, to an acquaintance for examining and reporting upon the same. These three embrace all the pieces into which this meteorite has been divided."

SECOND SERIES, Vol. XVII, No. 51.-May, 1854.

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