that it must arise from sulphate of magnesia being the agent by which the change into dolomite was produced. The magnesia of the sulphate of magnesia going to a portion of the lime to form dolomite (or carbonate of lime and magnesia), the sulphuric acid thus set free would form with water and another portion of the carbonate of lime, gypsum (sulphate of lime).

But chemistry had shown that when a solution of gypsum was filtered through pulverized dolomite, sulphate of magnesia was formed and carbonate of lime set free. Haidinger had also observed the efflorescence of sulphate of magnesia in gypsum quarries, and traced it to a decomposition of this character. As these last are results of ordinary exposure, Haidinger naturally inferred that this dedolomisation required no unusual heat or pressure, while for the inverse decomposition (or dolomisation), both heat and pressure might be necessary. Experiments on this point were projected in 1843, by Haidinger and Wöhler, but were not carried out. Von Morlot has at last applied this test, and confirmed the view so far as to show that when carbonate of lime and sulphate of magnesia in the requisite proportions are heated together under pressure, dolomite is actually formed, together with sulphate of lime. The temperature to which they were subjected was 200° C., and the pressure 15 atmospheres. An interesting problem was thus solved. [It is still a question, what is the least quantity of heat requisite for this dolomisation. Many compact limestones of our western states con. tain 30 to 40 per cent. of carbonate of magnesia, as first shown by Mr. D. D. Owen; and these rocks present no evidence of the action of heat. In the analysis of recent corals by Prof. B. Silliman, Jr., published in the volume on Zoophytes by the writer, there is less than one per cent. of magnesia. But in a compact coral rock made up of material of coral origin, he found 38-07 per cent. of carbonate of magnesia. The coral rock was a result of consolidation without heat, as we may judge from the absence of all evidence of its effects. Another speci men of a fragmentary character afforded 5.29 per cent. of magnesia. Both resemble the common reef rocks. They appear to show that there are circumstances in which the magnesian salt of the ocean, and the carbonate of lime of the corals, may react and produce a magne. sian rock at the ordinary tropical temperature of the water. This action may favor the consolidation into rock which is in progress beneath the seawater. It is evident that the finer the coral or calcareous material, the more magnesian the product; this principle accounts for the small proportion of magnesia in the second case alluded to above.-J. D. DANA.]

5. Three Minerals from the Lake Superior Copper Region; by J. D. WHITNEY, (Jour. Bost. Soc. Nat. Hist., v, 486.)-These minerals occur at Kewenaw Point, and on Isle Royal, where many zeolites have been found. The first of the three analyzed and described by Mr. Whitney, is Tabular spar. The other two are new species.

(1.) Jacksonite, (named in honor of Dr. C. T. Jackson.) It is near prehnite in composition, but contains no water. It occurs in finely radiated or lamellar radiated masses, of a white color tinged with green. H. 6. G.: 2.881. Translucent; lustre vitreous. Dissolves slowly but perfectly in muriatic acid, the silica separating as a flocky powder. SECOND SERIES, Vol. VI, No. 17.-Sept., 1848.

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Fuses very readily before the blowpipe in the platinum forceps, with a brilliant yellow light and a strong intumescence. Affords a colorless transparent glass with borax. Dissolves readily in a large quantity of soda; but with more soda, swells to an infusible slag. The analysis gave silica 46-12, alumina and a little peroxyd of iron 25.91, lime 27-03, soda 0.85 99.91, from which comes the formula Ca2 Si+Al Si. (2.) Chlorastrolite. This mineral occurs in finely radiated stellated masses, having a pearly lustre, and slightly chatoyant on the rounded sides. H.: 5.5-6. G. 3.180. Color light bluish green. Fuses easily before the blowpipe to a grayish blebby glass, intumescing and swelling up like a zeolite. In an open tube it gives off water and whitens. Soda dissolves it in small quantity, and gives a bead colored by a trace of manganese; with more of the assay it swells to an infusible slag. Dissolves readily with borax, affording a transparent glass colored by iron. Gives a beautiful blue with nitrate of cobalt. Dissolves readily and affords a flocky precipitate with muriatic acid. The analy sis gave silica 36·99, alumina 25-49, peroxyd of iron and a little protoxyd 6-48, lime 19.90, soda 3-70, potash 0-40, water 7.22 100-18. The following formula is deduced :—(Ca3, Na3)Si+2(Al, Fe)Si+3H : it is that of meionite, excepting the water.

6. Mines of Cinnabar in Upper California, (communicated for this Journal by Rev. C. S. LYMAN, in a letter dated Pueblo de San José, March 24, 1848.)-The mine of New Almaden is situated a few miles from the coast, about midway between San Francisco and Monterey, and in one of the ridges of Sierra Azul mountain. The mouth of the mine is a few yards down from the summit of the highest hill that has yet been found to contain quicksilver, and is about 1200 feet above the neighboring plain, and not much more above the ocean. This hill extends longitudinally in a northwesterly direction, decreasing in height; and in various parts of it, for several miles, traces of the ore have been found, and some openings have been made which promise to be valuable. This range of hills consists of a variety of rocks, which I have not yet had an opportunity properly to study. The prevailing one is a greenish talcose rock, which seems to embrace the bed of ore at the New Almaden mine both above and below. A specimen from the rock immediately contiguous to the ore, is contained in the box. The ore is interspersed through a yellow ochreous matrix, which forms a bed 42 feet in thickness, dipping northwesterly at an angle of about 45°. The richest ore, is at present found in the upper part of the bed, the poorer ores being taken from the lower portion.

This mine, known to the aborigines from time immemorial as a " cave of red earth," from which they obtained paint for their bodies, was first discovered to contain quicksilver about four years since, during experiments made by some Mexicans to smelt the ore for the purpose of ob taining gold, which they supposed it to contain. About two years ago it fell into the hands of Barron, Forbes & Co., who sent on hands, tools and funds to commence working it. Unfortunately the vessel fell into the hands of the United States forces, and was confiscated; the operations of the mine were of course delayed till the arrival of Mr. Forbes himself a few months since, with miners, tools, and whatever things he

was able to procure in Mexico, to enable him to make a fair experiment on the capabilities of the mine. The great trouble was to obtain suitable apparatus for extracting the ore. At length four potash kettles were found, which were set in a furnace of adobies, with condensers of mason-work immediately adjacent-a wretched apparatus indeed for managing so subtle a thing as mercurial vapor. While I was at the mine, the daily mode of working was to fill these pots in the morning with 1600 lbs. (400 to each pot) of the ores of average quality, broken in lumps of the size of apples, put on the covers and lute them with a layer of sand. The fires were then kept up till near night, when the furnaces were allowed to cool gradually. The next morning the condensers were opened, and the metal dipped up; which usually amounted to from 200 to 300 pounds for the four pots. This was a much less per-centage than the assay indicated, and it was obvious that a large portion of metal was lost. The upper parts of the pots and condensers were found to be generally coated with a crust of sulphuret of mercury, of which No. 15 is a small specimen. Mr. Forbes wished to devise some way of extracting the metal without mixing lime with the ore in the roasting, but was unsuccessful. At length a kiln of lime, which occurs in the immediate vicinity, was burned, and I am informed that, mingled with this, the ores yield a vastly larger per-centage of metal. In the last three weeks, about 10,000 pounds of metal have been extracted with the same apparatus, being a yield of over 50 per cent. Whether the ores were picked or not, I cannot say, but presume they were. Between 15,000 and 20,000 pounds have been extracted in about two months, only six miners having been employed in digging the ore, and the hands of the establishment, all told, miners, furnace men, wood-choppers, &c. &c., numbering only a score. The mine is probably yielding a nett profit of $100,000 a year, with its present crude apparatus. With suitable furnaces and iron cylinders or retorts, the mine would easily yield $1,000,000 and upwards. Mr. F. sails to Europe shortly for the apparatus necessary. The bed has as yet been followed but a few hundred feet, but the ores grow more and more rich and abundant.

The other mines opened in the vicinity, have not yet been sufficiently developed to decide upon their character. Ore has been found in fifteen or twenty other places within a few miles around, and within a few days in hills that do not seem to belong to the same range with that which contains the mine already described.

Some ores of silver have also been recently discovered in this region. But I have had no opportunity of procuring any genuine specimens as yet, and whether silver mines worth the working will be found, is at least problematical.

There are traces of coal in the country, but nothing of value has yet been discovered.

Gold has been found recently on the Sacramento, near Sutter's Fort. It occurs in small masses in the sands of a new mill race, and is said to promise well.

7. Argentiferous Galena and Iron Ore in Algeria, (L'Institut, No. 748.)-From a work on the mineral riches of Algeria, by M. Henry Fournel, we learn that there is a valuable mine of argentiferous galena

at Kefoum-Thaboul, near the frontiers of Tunis, occurring in argillaceous schists connected with sandstones and conglomerates.

Magnetic iron ore abounds in the mountains Bou Hamra, the small chain Belelieta, and to the north of lake F'zara. To the north of the place last mentioned there is an entire mountain, the Mokta-el-Hadid, which rises out of the gneiss to a height exceeding three hundred meters, and presents, from top to bottom, pure ore without a particle of rock. Remains of ancient Roman works and scoria were found, indi. cating that they were formerly mined.

8. Emery in Asia Minor.-M. Tchihatcheff, in his recent explorations in Asia Minor, has brought to light extensive beds of emery in the western portions of this country, particularly between the ruins of Stratonicea in Caria and Smyrna.

9. Fossil Footprints; by DEXTER MARSH, (in a letter to the Senior Editor, dated Greenfield, Mass., May 20, 1848.)-I have for a long time thought of sending you some account of my explorations in the rocks of this valley, and my success in obtaining fossils, but have hesitated from reasons unnecessary for me to state, knowing as you do, that I am an unlearned, laboring man.

You will recollect that the first specimen of fossil footprints of birds ever brought into public notice in this country, was the slab I discovered among the flagging stone, while laying the sidewalk near my house, which Dr. Deane first described to President Hitchcock, as the footprints of birds. Since that time I have felt an increasing interest in the subject, and have spent much time each year, in searching for these interesting fossils, and you will be able to judge of my success, when I tell you that I have in my collection more than eight hundred footprints of birds and quadrupeds, besides having furnished specimens to many individuals and institutions in this and other countries. I have some very perfect tracks of a quadruped so small that a five cent piece will more than cover the entire impression of the foot, and the tracks of a bird that measures more than half a yard from the heel to the point of the longest toe, with the foot very thick and heavy in proportion to the length. The most perfect specimens. I have been able to obtain, are from Turner's Falls, or its immediate neighborhood; they not only show the joints of the toes, but in some specimens perfectly exhibit the impression of the skin.

I have obtained also valuable specimens at other places; for instance, a very interesting slab at South Hadley, found in the highway leading to Amherst, a mile and half north of the Seminary. It is in a coarse gray sandstone, cut and used for building purposes; the quarry was opened for that purpose, and a few tracks discovered before my atten tion was called to it; the beds containing the tracks lie some three feet deep, and are nearly horizontal. I quarried a small section, and turned up a slab seven or eight feet in length by one and a half in breadth, having on its under surface fifteen or twenty beautiful footprints of a number of different birds in relief. I then thought by taking up a large section, I should obtain all the tracks I desired; but to my great disappointment, after several days labor in getting down to the same layer, not the slightest appearance of a footprint was to be seen. I then examined the location more particularly, and to my mind it was

easily explained; the material of which this rock is composed, was deposited by running water, which accounts for its being so coarse, all the finer particles being carried away but after the water had subsided, there seemed to be a depression, or small basin, but a few feet in diameter, where the water was left to evaporate, depositing a thin layer of fine light colored clay, over which the birds walked. The impressions in this layer were very beautiful, but they could not be preserved, as the matter did not harden into rock, but was easily removed with the shovel. This is precisely like what we often see by the roadside after a heavy rain, where the water is left in small ponds to settle and evaporate, leaving a fine deposit, on which we often find the footprints of birds.

I have obtained at the south part of Montague some hundreds of footprints of birds, and some species that I have not seen at any other location, but have met with no quadrupeds. This location is more than half a mile from the river, and nearly two hundred feet above it; the tracks at this place are not as perfect as those I have obtained at the Falls, in consequence of the surfaces over which the birds walked being destitute of that smooth polished appearance that is necessary to receive fine impressions, though I have some specimens that are good. But some of the largest (and most perfect for large ones) I have ever seen, I obtained on the eastern declivity of Mount Tom, near South Hadley Falls. If the height of these birds was in proportion to the length of their feet, when compared to some existing birds, they must have stood some twenty feet high. But the rocks of this place are too coarse to have retained fine impressions of small birds or quadrupeds, for when the matter was deposited, the water was in continual motion, so as not to leave smooth surfaces to the strata. I have one slab containing two footprints of a large bird, the surface being very rough and uneven; but the great weight of the bird (probably a thousand pounds or more,) pressed the sand so hard that it is perfectly smooth, showing distinctly the structure of the bottom of the foot.

I have many specimens from Wethersfield, Conn., which show very plainly that they are the tracks of birds; still I consider them imperfect because they do not show where the bottom of the foot rested. The deposit seems to have been a fine reddish clay, so soft that the bird settled down a number of inches, the mud closing up again when the foot was withdrawn, leaving no depression on the surface; the tracks are seen only by splitting the strata, through which the foot passed.

I have at some localities traced the tracks of a single bird thirty or forty feet, when the bird went into the water; this I know from the fact, that the first tracks would be very slight indeed, being pressed on hard sand or clay, and each successive step would be deeper and deeper, until the mud closed over the impression; and when he got into the water, though he settled deep in the mud, the motion of the water entirely obliterated all appearance of the track on the strata over which the bird had walked. But by removing a thin layer we find the impression. This has oftentimes enabled me to ascertain how high the water was at the time, or how much of the layer was out of the water when the impressions were made.