a future work after having visited again these distant regions. I shall seek to establish at the same time, in a most precise manner, the relations which exist between the trap and conglomerate; for these relations only can establish the point whether the trap of Lake Superior has really been in perfect fusion, or if it should be regarded as a metamorphic rock, representing the graywacke of Europe.

(To be Continued.)

ART. VI.-THE COPPER VEINS OF THE SOUTH.-BY OSCAR M. LIEBER, Assistant Geologist to Alabama.

WHAT are true veins? is a question, the answer to which is of the utmost importance to the practical geologist or scientific miner, and yet we find it very differently and frequently somewhat unphilosophically answered. Some define veins as bodies of rock, whose dip or strike is at an angle with that of the strata of the circumjacent rocks, so that the same bed may, if we adhere to this definition, be a vein at one point and an ordinary stratified bed in another. I believe it was Werner, however, who already observed that indication of a secondary formation, of an origin subsequent to that of the neighboring rocks, is a necessary characteristic of veins. It matters little whether or not the mere external features of strike and dip are conformable to those of the beds through which they pass; and, indeed, it would be difficult to point out an instance where, in depth, the vein does not gradually assume the dip of the rocks of the country. An explanation of this phenomenon is not difficult, when we reflect that veins are simply crevices, subsequently filled. Whatever may have been the originating cause of these fissures-elevation of the rocks or gradual contraction of our globe while cooling, and consequent breaking up of its crust-it is very easily conceivable, that the surfaces of the beds, being the points of less intimate union, would be the ones most liable to rupture, and that, with but few local exceptions, the fissures would follow their course.

We find, as a general rule, that near the surface the veins are irregular or split up into a number of smaller ones, which the miner terms "feeders" or "leaders." We have hère, an instance, but on a grand scale, of that which we find in the rupture of any earthen vessel. On the outside the crack is irregular, and small pieces are entirely severed from the main body.

In some instances it may be difficult to determine by superficial examination whether a bed is a vein or not, where no peculiar orographic features are discernible. Nothing will then

suffice but an investigation of the oryctognostic characteristics made at a depth where their peculiarities are sufficiently developed, and where the nature of the bed may be ascertained from the mineral composition or the orographic distribution of these ingredients.

An interesting case, where the writer was at first inclined to believe a bed, of regularly stratified origin only, existed, is to be found in Talladega county, Alabama, where they are at present making experimental investigations for copper. A more careful inspection, however, proved that this was really a true vein. In the first place we have the repetition of the solid quartz on both sides, an instance of that singular parallel disposition of the ingredients of veins, which has led Cotta to found his famous theory explaining the origin and mode of introduction of the minerals now filling the vein crevices. In the second place we find a singular asbestiform variety of quartz, which consists of long imperfect acicular crystals, standing at right angles to the dip of the rocks, and which would therefore also induce us to believe that it must have been deposited in a crevice, and hence subsequent to the formation of the adjoining rocks.

Another remarkable instance of this group of veins is to be found at the Waltruss mine, in Polk county, Georgia, where of one lode no outcrop was observable, and where it was found in sinking a shaft to strike an entirely different vein, which is below this, and will, in all probability, join the main body. The latter is at present fifteen feet thick, though mixed with slate on the hanging wall. The foot wall is quartz, the upper part of the vein iron pyrites, while at a depth of about thirty-five feet the copper first makes its appearance in noticeable quantity, entering in irregular masses. It is very probable that at a comparatively insignificant depth very valuable copper ore will be reached, since already such unexpectedly fine results have crowned their desultory operations.

I have not myself visited the mines of Ducktown, in Tennessee, as yet; but all descriptions seem to point to a great similarity of their characteristic features to those of the Georgian mine just described, although there in most cases they find a black cupriferous mineral, consisting of impure black oxide and sulphate, between the gossan which forms the iron hat and the undecomposed sulphurets of iron and copper.

The gossan is a silico-ferriferous mineral, which presents very distinct appearances in different localities. Thus at one time we find it cellular, at another compact, at a third lamellar. Sometimes it is friable, sometimes solid. In some places it seems to be arenaceous, at others it consists of a cemented breccia of the slate and quartz, the cement being impure peroxide of iron. In many cases this compound rock is doubtless of later origin, a secondary formation, in which the iron cemented together broken pieces of

the "country" rocks. At first I was inclined to believe that this was the case with all of it, though lately it has become very evident to me that much of it belongs to what German miners term "Gaug-Trumm," (from trimmer, ruins, and gaug, vein) and which we also find far below the surface in the veins. Meeting with so much slate too at the Waltrup mine, mixed with the copper and iron pyrites, we perceive also another source whence these imbedded irregular or breccia-like pieces of schistose rock may have been derived; so that, indeed, in many instances they may still occupy their original position, being merely surrounded by the hydrated peroxide of iron, derived from the pyrites. "Gossan" is a term, referring only to the oryctognostic features of the mineral, although it has latterly been used as synonymous to the German word "Eisen Hat," iron hat; a term descriptive of the orographic character. Sometimes the outcrop of such veins is a cellular quartz, itself of a pure white, but colored superficially by peroxide of iron. Mr. Dury of Alabama, who has devoted much time to the study of this group of veins, is of opinion that the shape of these cells may afford us some light in judging of the character of the veins in depth. This view is based upon the well-ascertained fact that a mineral, which crystallizes according to various systems, as for instance sulphuret of iron (rectangular and rhomboidal), will, as a rule, retain that form throughout in the same vein. Only where the iron pyrites crystallized differently from the copper ore would it be possible to find a guide in this. If both crystallize in octahedrons we shall not be able to distinguish their impressions, but if the iron pyrites is of the rhomboidal variety, and we find among the cavities not only rhomboidal cells, but also octahedral ones, then, according to Mr. Dury, we may expect to find copper. These views are very sound ones; and we but need greater experience to ascertain whether they are true in all cases; since he has communicated his theory to me, I have, where it was possible to test its correctness, found it to be true.

The same gentleman, who has examined these veins from Virginia down to their south-western terminus, believes that they are confined to the intermediate space between the Alleghanies and Blue Ridge, and that the extensive group of veins described by me in the "New York Mining Magazine" for October, 1855, and characterized by gold, lead and copper, with a highly quartzose gangue, never encroaches upon the region occupied by the other group. As distinct names will be of importance, as rendering tedious descriptions unnecessary, I would suggest that we term the former the Ducktown group, from the well known mines of Tennessee, where they were first opened; the latter the Carolina group, since in the two States of this name it seems to be most perfectly developed.

Let us now review what appear to be the chief characteristics
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of this Ducktown group as far as our present very limited knowledge of them permits us to decide.

First is the slate or other country rock, then the outcrop of iron ore or gossan, sometimes here, from subsequent action, more or less stratified. At one point the gossan is certainly in place, and the vein "has formed;" i. e., its wall is distinctly discernible. Farther down is black oxide and sulphate of copper, greatly adulterated by silica, &c.; still farther is the undecomposed portion of the vein, and consists of a solid mass of sulphurets of iron (in Ducktown arsenical pyrites?) and copper mixed with quartz, the copper increasing in quantity downwards. As footwall we find a solid quartz with some sulphurets. Nearer the surface the rocks are decomposed and the stratification indistinct by surface action.

Now it is very evident that at one time the whole of the metallic portions of this vein were pyrites, and that atmospheric action produced sulphates and oxides. The iron, in the shape of sulphate, was in part leached out and gave rise to the stratified deposit in many instances worked for iron. A portion of the sulphate and black oxide of copper collected lower down and formed, as it were, a bed in the vein, though deposited irregularly and frequently only on the footwall. This is the ore which was first worked at the Tennessee mines. When the gossan is in place. (though it is not found in all instances), we find the vein in its original state, the copper increasing in quantity in depth, and those examinations which I have been able to make latterly, have certainly induced me to believe that there will yet be discovered vast storehouses of nature, which will at a future, though I trust not distant day, do much towards furnishing the world with the necessary amount of this valuable metal.

Although, strictly speaking, the only true ore of these mines, or at least the only one whose persistence we may depend upon, is sulphuret of copper, still we meet with other cupriferous minerals also. The sulphate and impure black oxide have already been mentioned. The red oxide occurs in some instances, as at Gamble's mine in Polk County, Georgia, while native copper, a galvanic precipitation from the sulphate and hence of secondary origin, is met with for instance in the mines of Ducktown, and at M'Gee's in Talladega county, Alabama. Carbonate of copper of the green variety has formed in many instances near the surface or on exposed specimens of the black ore, and the hydrated silicate of copper or dioptase of the Germans is found also, though rarely. With the exception of the latter, these minerals are all the direct or indirect products of the decomposition of the pyrites and of but little practical importance.

Undeveloped as these treasures still for the most part remain, we see already that the Blue Ridge is, probably, but the dividing line between two groups of veins seemingly almost unparalleled in

extent, and that, in all probability, our Southern States may congratulate themselves upon being most munificently provided with

"Plenty of the rarer, milder ore

Of which the early Roman forged his sword,
And Greece, undying, her creative chisel."

ART. VII.-FOSSILIFEROUS FORMS IN EASTERN MASSACHUSETTS.*

PROF. WILLIAM B. ROGERS exhibited to the Society several specimens of rock containing casts of portions of a large Trilobite lately obtained by him from a locality on the north edge of Braintree, about ten miles south of Boston. He adverted to the great interest of this discovery, as furnishing the first clear evidence yet obtained as to the geological age of any of the extensive series of altered rocks which occupy a large part of Eastern Massachusetts and the neighboring States.

Hitherto geologists have not been aware of the existence of any fossil forms in these strata, as none are referred to in the Geological Report of Prof. Hitchcock, or in any of the subsequent publications relating to the rocks of this region. The present discovery, therefore, will be a matter of surprise as well as gratification to those who have given attention to this obscure and hitherto unproductive portion of our geology.

It is true, that in view of the lithological characters of these altered rocks, and their relation in strike and position to the carboniferous strata adjoining them towards the S. W. in the contiguous parts of Massachusetts and Rhode Island, they have of late been considered as probably belonging to parts of the Paleozoic series inferior to the Coal Measures, and including portions of the Devonian and Silurian systems. But the want of any positive evidence derived from fossils has, until now, left us without a clue to the actual Paleozoic age of any part of the group, and has indeed given a character almost purely conjectural to speculations in regard to the epoch of the group at large.

In respect to the zoological relations of the Braintree Trilobite, Prof. Rogers remarked that from the imperfect examination he had as yet given these fragmentary specimens, he was disposed to consider it as closely allied to the forms of Paradoxides described by Green in his monograph, on North American Trilo bites. Of the two species described by Green, viz., P. Harland and P. Boltoni, only the latter has been recognized by Prof.

* Boston Society.-Nat. History.