remark, that the delomic limestone, which lies in the oldest clayslate near Tharand, just there where it comes in contact with the porphyry, very often contains, in rugs or druses, the crystals of iron and copper pyrites, galena, zinc blende, and heavy spar. Would it not be just to suppose that these minerals are here as well caused by the neighborhood of the porphyry as in the Freiberg mines?

[To be continued.]

ART. VI.-AMERICAN GEOLOGY.*

AMERICAN Geology, as such, has hitherto had no exponent, unless it is to be found in the work whose title is placed below. That it is there investigated, it will not be necessary for the reader to enter far in its pages to satisfy himself, or to become convinced that he has in his hands an able work containing novel views of a new subject, or perhaps it would be more proper to say, new and independent views of a great subject. The author writes like an able and independent thinker, fearless in expressing his views from a consciousness of innate ability to maintain them. He asks not for authorities, but seeks facts. He leans upon no theories, nor fortifies himself with any opinions unless they are sustained by the senses. It is this method of entering upon the investigation of American Geology, this disregard of anything like aristocracy in science, which we like, and the result is that we have a more clear and satisfactory statement of the principles of this science in the abstract, together with an exposi tion of it, than is to be found in any other of the numerous volumes issued from the press.

The work itself, of which the first part has just been issued, is published in a style unequalled by any scientific American work. The paper is no whit inferior to the best style of European books, and the execution is worthy of it.-The embellishments or illustrations, which have been executed on wood, stone, and steel, are among the very best of their kind. It truly affords a pleasing satisfaction to see that the value of such a style of publication is appreciated, and to know that the public taste of the day has compelled publishers very extensively to resort to the best skill and materials of their trade.

This undertaking is introduced to the public not with any extensive or explanatory preface, by way of an apology for

* American Geology, containing a statement of the principles of the science, with full illustrations of the characteristic American fossils. To be published in four parts, with an Atlas and a Geological Map of the United States. Ebenezer Emmons. Part I. 8vo. pp. 194. Albany: Gray & Sprague, and J. Munsell.

doing what should always be fearlessly done, but with a few sentences, modestly entitled, "Proposals," which are briefly as follows::

"The American Geology will be published in four or five parts, each of which will be illustrated by appropriate woodcuts. Each part will contain about two hundred pages of letterpress. The paper and press-work of the present part shows what the mechanical execution will be.

"The fossils will be executed on stone and steel by the best artists, and no expense will be spared to make the work complete. The present part, it will be observed, contains a fine illustration of the moon's surface, on stone, by Swinton, and a quarto plate, on steel, by our distinguished engraver, J. E. Gavit. The plates of fossils will be distributed with each part, but numbered for binding together in a uniform style with the geological map when the work is complete.

"I have no design to find fault with or disparage the works that have been published by our geologists, still it cannot fail to be observed that they are not American. We want an American Geology, and all necessary means will be employed to accomplish the purpose I have proposed.

"E. E."

The preliminary remarks with which the work commences are devoted strictly to the science of geology, and notice such points as are necessary to be understood, as lying at its base, and as exerting an influence throughout all its investigations. This is a part of a scientific method, and, likewise, indispensable for those less familiar with the general subject, at the same time it affords the ground for the distinctive features of every treatise. There may be many who will dissent from some positions of the author, but we doubt if they can combat them with better sense or more forcible logic. Take the doctrine of progressive development for instance:

The life of plants and animals is controlled by a single element; that is, oxygen. The adaptation of organs is in accordance with its properties. It has always been so. We presume, too, that its supply has been constant-that there has been no period when its quantity was either greater or less than it is now. A different view is not sustained by the fact that at one period huge lizards predominated in its fauna, for analogy proves that this class would have perished with a less proportion than that which exists in our atmosphere at the present time.

In cases of this kind, reasoning from special structural affinities to general physical conditions is not always safe. The lias and oolitic periods abound in the remains of cold-blooded animals, whose respiratory apparatus was undoubtedly imperfect, like the lizards of the present. It is a favorite inference with a certain class of the progressive geologists, that the oxygen of the atmosphere at that period was less in proportion to its mass than it is now. But then may we not inquire, if there was less oxygen in the present atmosphere than there actually is, could the menbranous reptile lung supply the demands of the system; and is not the constituent proportion of oxygen the

quantity required to give the creature the power to breathe at all? I say it is not always safe to reason from structural affinity to physical conditions. If we take any other organ, as the eye, and draw from its structure and condition analogous inferences concerning the quantity of light, we may see where it will lead us. A class of progressive geologists, maintaining that in the early periods of life the light of the globe was dim, and that but few rays shone through the hazy atmosphere, find in support of this doctrine the fossil remains of a fish or a lizard with enormous eye sockets. He believes that the large eye was adapted to a dim state of the atmosphere. Another person finds a fossil with very small bony sockets. In this case, too, it may be said the eye was very small, and hence it was adapted to an exceeding intense light-to the sun when it shone fiercely from its throne in the heavens. But again, a fossil is found entirely destitute of an eye socket, and not a vestige of an organ of vision can be found; hence, there was a time when the earth was shrouded in darkness, for in darkness animals have no need of eyes, and light would be useless to animals destitute of the visual organ. But then we find all these states of the eye in the present arrangements for supplying the world with light. The Pomatomus telescopium, a fish of the Mediterranean, which lives in very deep water, has a remarkably large eye. It is the position which it occupies that requires the large eye, and that large eye is adapted to its abode; and if only one-half of the light of the sun was extinguished, it probably would be unable to see at all. And just so with the reptile, if one-half of the oxygen of the atmosphere was withdrawn from it, all reptiles would die. The mole has a very small eye, but that small eye would be of no use if the ground was lighted by fewer rays. The blind fish and the blind animal of the mammoth cave live in a period when the earth is lighted up most gloriously their abodes are dark, but yet the sun shines without in all its strength. We find, then, all conditions of the eye and the lungs at the present time. But it does not follow, that because the structure of the fossils of a given period may be found whose organs belong to a certain type, that the physical conditions of the earth were materially different from what they are now. This view of the subject does not conflict with the doctrine of adaptation, but rather sustains it. The physical conditions are first established; the organic kingdoms afterwards come in with their separate adaptations. The organisms are perfect in their adaptation to the conditions in which they are to live, as well as to the position in space, and the mediums in which they are to be placed. The doctrine of progressive development, as usually represented, seems to be untrue. It proceeds on the ground that the earliest beings were the least perfect, and that progression consisted in the creation of those animals which were more perfect in their structures than their predecessors. But who cannot see that the world is full of the same imperfections in animals now as in the beginning. Progression has no reference to perfection of structure, but to rank. Structures have been always perfect, but rank has been progressive.

The nomenclature adopted in this work contains some decided improvements; there is, however, room for more, which we hope to see at some day introduced. As here presented, it is clear and comprehensive. The rocks called metamorphic or azoic are not recognized as classes, or even subdivisions of sections, inasmuch as they have no special peculiarities which make them applicable for such purposes. Metamorphism occurs, or may occur, in all the series of rocks from the earliest to the latest sediments. It is true that the term metamorphic has been confined to gneiss, mica slate, hornblende, talcose slate, &c.; but its use is theoretical, and was thus applied on the hypothesis that

those rocks are altered sediments, of which there is no evidence. The term azoic presupposes that our observations have made certain that which from the nature of our evidence must ever remain doubtful. There is no doubt but that granite gneiss, mica slate, &c., are azoic, but no one would think it proper to apply it to those rocks. The following is the nomenclature adopted:

The remainder of Part I. is devoted to descriptions of the rocks, commencing with the Pyrocrystalline, and closing with the Pyroplastic, as they are developed in this country. There are many interesting points here, to which we would like to bestow, at least, a passing notice, but must refer the reader to the work itself, with accompanying illustrations. The latter portion of this Part is devoted to the subject of mining, &c., embracing nearly sixty pages, and to this portion we shall confine our further remarks.

The term "mining," in the comprehensive sense here used, is treated of under the following heads.

1. The theory of the formation of those depositories which contain the metals and ores.

2. The structure of those depositories.

3. The changes which the mineral undergoes in depth.

4. The best modes for extracting their metals and ores, including those which have been devised for raising blocks of rock from their beds.

5. The expense attendant upon different kinds of work in mining and quarrying.

6. The value of the products of mining.

In the explanation of the theory of the formation of those depositories which contain ores, there is much which is of interest, of which, however, we can only take a passage or two:-

In the first place, we must look upon all the repositories of the ores and metals as ancient arrangements, by which they are made accessible to us; and that those arrangements are the necessary result of the constitution of the globe. They are by no means to be regarded as accidents, arising from conditions which might have been otherwise. They, too, are general results, confined to no limited scale; and when the forces and plan were determined, upon which to form and fashion the earth, the results of which I have spoken became an essential part of those causes, and it would have required special instrumentalities to have prevented their operation just as we now see them to have operated. It is for this reason that the formation of repositories for the metals has been controlled by law, by which certain constants may always be looked for. This being the case, the miner has not overlooked the plainest of these results, but is constantly referring to them in his operations with confidence.

It is not necessary that we should connect these laws with the early conditions of the globe in order to understand them; but as facts it is proper that they should be borne in mind. What was that original condition, then, which gave birth to the repositories of the metals? It was that incandescent state of the crust of the globe, of which I have already had occasion to speak. We have no occasion now to inquire what gave birth to that incandescent state; the fact is attested in the phenomena everywhere visible in those portions of the earth's crust which belong to its earliest epoch, The most important effect of this state is the expansion of the crust, or the occupation of a larger space for the time being. But the earth, situated in space, and in a colder medium than itself, has necessarily lost that primitive heat which belonged to its earlier stage of existence. It has cooled, and the most important result which interests mining is the consequent contraction of the cooled part. Contraction has severed the bonds of the continuity of the strata; and those fractures which are the result of the cooling process have been made in comparatively straight lines, or in given directions; or we may regard the causes of fractures simply as subterranean, but due to general conditions, and which must necessarily affect the whole of the cooling envelope.

The fact that fissures may be, and probably are thus formed, is agreeable to all that is known of cooling bodies; and observation which has been directed to those fissures proves, in the general at least, that the fissures are made in lines of bearing quite constant. We may not infer that a mechanical force is applied beneath a stratum, and has erupted those strata in the lines I have spoken, as a previous step in the formation of a vein. A cooling state has given rise to a state of tension, which increases in the direct. ratio of the diminution of temperature, which is finally too great to be borne, when the continuity is broken. It is true that a subterranean force is often operative in the mode represented, and by which strata are uplifted and fractured; but it is more consonant to facts to suppose that vein fissures are the result of cooling and the great tension which arises therefrom. As a general rule, the direction which a fissure has taken was in a line of the weakest part of the stratum; but it is easy to conceive that a greater strain may be made upon a stronger part, so as to form a fracture in a line which is apparently along the strongest part of the stratum. In crystalline rocks the planes of lamination must be regarded as weaker planes, and hence it is that a very large proportion of our veins of magnetic iron lie along those planes.