the labors of Brewster, Haidinger, and especially G. Rose, have been brought under a regular law, the subject has not been exhausted. The memoir of M. Descloizeaux affords means of judging on this point.

M. Descloizeaux has examined many crystals from various localities, noting that each locality has its characteristic forms. He has made out many new planes, increasing the number of observed rhombohedrons from 13 to 60, and of plagihedral planes from 23 to 66. In the rhom bohedral series, he finds only 17 which coexist with the corresponding inverse rhombohedron; and in the plagihedral series, only 8, that have also the inverse. These facts, together with the different aspect and physical properties of the faces, are regarded as proving that the fundamental form is a rhombohedron instead of a hexagonal prism.

Besides the forms mentioned, M. Descloizeaux has made out many others which appear to require to be taken into account in the study of the geometric configuration of quartz, as they are regular and well defined, yet have quite high numbers in their crystallographic expressions. It is probable that these complex forms will increase as crystallography is more studied. The study of these facts, lying on the limits of pos sibility in crystallography, are of peculiar interest to the science. The preponderance of the regular forces is shown to be in a weakened state, permitting the effects of external perturbative influences. The same cause accounts for the frequent imperfection of the more com. plex forms and the variations of angle-imperfections seldom observed among the more common forms. M. Descloizeaux has given his measurements of these exceptional cases without disguising the discordances between calculation and measurements.

The pretentions, now common with regard to the absolute exactness of crystallographic observations, leading to the use of the method of least squares for estimating the probable errors, are a pure illusion. It is easy to show that artificial crystals are altered in angle by extraneous causes, foreign to the molecular forces; and it is impossible that natural crystals should have escaped like influences. When the number of minutes is somewhat uncertain, it is not reasonable to attach so much value to seconds: a number is reached; but when the anomalies are in the nature of the thing, it is only self-deception. The divergences have causes, which are to be discovered; and it is the great problem to ascertain the limits of variation, and not blindly to assume an illusory coincidence in accordance with the abstract law of Haüy.

The new faces determined by M. Descloizeaux have much increased the possible geometric elements of hemihedrism, with which the circular polarization appears to be connected. Twenty-four plagihedral faces are now known to occur either in the right-hand or left-handed spiral. M. Descloizeaux here inquires, what particular optical effect may be connected with each of these plagihedral forms. After numerous observations, he concludes that, with one exception, the facts thus far ascertained afford no absolute conclusion, and only suggest some probable inductions.

M. Descloizeaux next takes up the macles of quartz. He shows that they often obey only approximately the absolute law of twin-composition, the angles sometimes varying 2° from the theoretical value. This shows that the forms are not held inflexibly to a geometrical law; that the physical laws express only the limits of stable equilibrium

towards which the condition always tends, but from which it may diverge considerable from external causes, without destroying altogether the equilibrium.

The subject of composition by complete interpenetration and the soldering of crystals occupies much of M. Descloizeaux's memoir. The crystals are united irregularly, almost as if melted into one another, the union being in an exceedingly complex manner. These forms were well illustrated by Mr. Gustav Rose. But M. Descloizeaux has examined them by sections in various directions, and studied both their crystalline appearances and their optical characters, finding sometimes a mosaic interior.

The various appearances are shown in the engravings. The effects of polarized light were obtained by means of photography.

Plates cut from the extremities of the same crystal have rarely the same structure, and almost always show a more or less complicated arrangement of plates of contrary rotation.

The planes of composition are usually parallel to the faces of the pyramid, more rarely to the rhombic faces of Haüy; sometimes parallel to the faces of the hexagonal prism or some very acute rhombohedron. The arrangement of quartz of inverse rotation in layers parallel to certain faces of the crystal seems at first to accord with the law of increment. But how can we explain the direction of the different colored strata, when the parts of different rotation, while being still in regular layers, cross other plates often in opposite directions? when the layers have regular contours and divide the interior of the mass into compartments with a symmetry which cannot be mere chance? Photography has been of vast service to this subject by the fidelity with which it registers the facts. The plates are numerous and of the highest interest.-L'Institut, No. 1117.

3. Note on Heulandite and Scapolite from Arendal, by E. ZSCHAU. -From the chemical composition of the varieties of these minerals which occur at Arendal may be noticed an interesting analogy. The following analyses (1, 11) of Scapolite are by von Rath, and (111) of Heulandite by Sjögren.

The basic nature of Scapolite and the more neutral of Stilbite point out clearly that the excess of the bases in the former has been removed by atmospherical agencies, giving as products the more neutral and stable compound, Stilbite. The alkalies of the Scapolite have entirely disappeared, as well as a large portion of the earths.

This view is supported by the fact that the Heulandite of Arendal (Barboe Mine) always occurs either upon or near Scapolite.

4. On a Twin Composition between Malacone and Xenotime, Apatite, or Monazite; by ERNST ZSCHAU, (communicated by G. J. BRUSH.) It is an interesting question whether crystals of different kinds can form twins with one another. The annexed figure of an actual crystal from Hitteröe, is an exam. ple of two species thus combined, both of the dimetric system, the prism being zircon (Malacone), and the octahedral part below, Xenotime; the two are homoeomorphous, 0:1 being 138° 45′ in Xenotime, and but little less in Malacone (138° 15').

Malacone also occurs at Hitteröe compounded with apatite and monazite. The O on 1 in apatite is 136° 47'.

5. On Prosopite; by GEO. J. BRUSH.-Prof. Scheerer has shown that the so-called "Speckskein" pseudomorphs from Altenberg in Saxony, have the composition of Kaolin, and that the crystals although homœomorphs, are not pseudomorphs of Barytes as suggested by Breithaupt;-the original mineral being, according to him, a fluorid of aluminium and lime, with water, to which he has given the name Prosopite.

Subsequently Prof. Dana pointed out its homœomorphism with Datholite, and suggested that Prosopite might possibly be an altered Datholite. Through the kindness of M. E. Zschau of Dresden, I was put in possession of a number of crystals of Prosopite, which, although presenting the same crystalline form, had such a diversity of physical characters, that I was led to give them a chemical examination, to ascertain if possible the true composition of the unaltered mineral.

Owing to the small quantity of the mineral at my command, the results obtained are for the most part incomplete.

The physical and chemical characters of the crystals were as follows: Color light violet and transparent to white and opaque. H. from 4 to so soft as to be easily scratched by the nail. Lustre brilliant to dull. The violet crystals had a hardness of 4, sp. gr. 3.177, a brilliant lustre, and a distinct octahedral cleavage; they contained no water and were composed of pure Ca Fl and a trace of organic matter. A quantitative analysis, made by decomposing with sulphuric acid, gave on 141.5 milligrammes of mineral employed, 242 milligrammes of sulphate of lime, equal to 71.44 milligrammes or 50-49 per. cent. of calcium. The result of the decomposition by sulphuric acid was completely soluble in water and the solution gave no reactions for any other base but lime. The crystals which had a less brilliant color and a diminished hardness contained more or less of a hydrous silicate of alumina according to the extent of alteration they had undergone, the results of complete alteration being pure kaolin as shown by Scheerer.

In all of the crystals that contained even traces of water, alumina was also found; and although silica was not in each case detected, there can be little doubt of its presence, as the change from fluor-spar into

*Poggendorff's Ann., xc, 315.

SECOND SERIES, Vol. XX, No. 59.—Sept., 1855.

35

kaolin can be so distinctly followed. (Where fluor-spar predominated in the mineral silica might be easily overlooked as when decomposed by sulphuric acid, it would be evolved in the form of gas in combina. tion with the fluorine. I confess I had neither apparatus nor sufficient quantity of the mineral to investigate this point as accurately as it deserved.)

This unexpected result made it of importance to determine with accuracy the form of the crystals. For this purpose all of the specimens in my possession were forwarded to Prof. Dana who has had the kindness to examine them and communicates herewith the result of his examination. The violet crystals were in some cases accompanied by massive fluor, in others imbedded in Hematite.

In connection with the above results, my attention was called to the fluor of other localities, particularly that of Zinnwald and Graupen. At Zinnwald the cubical crystals of fluor are sometimes altered into a substance resembling Speckstein; on analysis this so-called Speckstein proved to be a hydrous silicate of alumina and the partially altered crystals had the same composition as the Prosopite before examined.

With the Cassiterite at Graupen in Bohemia is found fluor-spar and a compact white mineral which has heretofore been called Speckstein. This latter is a hydrous silicate of alumina and the same stages in the passage from fluor into this substance may be observed here as have been described with the Prosopite crystals. Specimens of fluor from Nieder, Pöbel, and other localities near Altenberg presented the same peculiarities.

From these facts it seems that fluor-spar is liable to alteration into kaolin, and that much of the so-called Speckstein is really a hydrous silicate of alumina.

I regret that it is not in my power to give a series of quantitative analyses showing the gradual passage of the fluor into kaolin, and I only offer this brief notice of my results in the hope that it may be the means of calling the attention of some chemist to the subject who may have an abundance of the mineral and a laboratory at his command. Freiberg, July 16, 1855.

2 2

21 23

NOTE BY J. D. DANA.-I have examined the crystals of Prosopite sent me by Mr. Brush, and find the external characters and cleavage confirm. ing fully his statements. The form presented, is well shown in the figure in my Mineralogy, 4th ed., p. 502, (here repeated) which is drawn from Scheerer's but in an altered position, and there is little variation either by distortion or otherwise. It is hemihedral trimetric, like Datholite. I have endeavored to reconcile the form with a distorted monometric crystal; but the persistence and regu larity of the form in all the crystals, is against the idea of its being a distortion. Moreover, if a twin, composition must be parallel to it; and this view is opposed by the inclination of it to the planes around it, and still more by the cleavage, which cuts through the crystals without any reëntering angle or line of interruption. The cleavage affords in fact regular tetrahedrons and octahedrons with the same facility as fluor spar; and no one of the faces of cleavage in one crystal was

ཨཱ

23

ii

parallel to it, or to any other occurring plane. Moreover the cleavage planes had no symmetrical arrangement with reference to the axes of symmetry in the crystal.

Although, therefore, the violet crystals are monometric fluor spar in cleavage and other characters, I am not satisfied that the external form is monometric in origin; it may be pseudomorphous after some species not yet ascertained.

Several of the crystals have the edge between the two planes iğ beveled by two planes I, which according to my measurements, (approximations only, as the faces do not reflect a distinct image and are often uneven,) incline to one another, 113° 30'. I obtained also i2: i2 =74° 30′, 1:12 = 150° 45′ ; ii: x (unlettered plane) 104° 30′; 2:2 = 131° in one crystal; 133°-134° in another; (and the latter crystal afforded also 2ř: 2i = 118° 15'.) In one specimen there is a plane replacing the edge it: 2, giving for the inclination on 27 approximately 149° 30; it is probably the plane 67, following the lettering in the figure. The plane 23 is usually uneven; and there is sometimes another between it and 27.

One of the Prosopite crystals is violet fluor at one extremity and white like a kaolin at the other.

6. Note on Geology of country East of Cascade Monntains, Oregon, (extract of a letter from GEO. GIBBS, Esq. dated Steilacoom, Washington Territory, May 7th, 1855).-Dr. George Suckley, Assistant Surgeon U. S. A., stationed at the Dalles of the Columbia, Oregon, has recently made an important discovery bearing upon the geology of the country east of the Cascade mountains, of which, although the details are as yet but imperfectly ascertained, we think a notice will prove interesting. It is the existence of extensive strata of fossiliferous limestone lying between beds of basalt. The limestone appears to be protected in places by a layer of river stones and gravel, and elsewhere to be metamorphic. The order of position descending is as follows. 1st. Sand and superficial soil 1 to 10 feet; 2nd, basaltic rock 3 to 10: 3d, cobblestone and pebbles; 4th, limestone 6 to 8 feet; 5th, cobble stones, &c.; 6th, basalt. Among the fossils are bones of mammalia, some of them gigantic. They are brittle and require great care in removing, and as yet no examinations have been made to ascertain their genera. These bones are also found near Fort Wala-wala, at the junction of the Snake and Columbia and are said by the Indians to be common there. No fossilliferous rock has heretofore, it is believed, been found in any place between the Blue Mountains and the Cascades and the rarity of organic remains, in that region has been the subject of remark. This dis covery will throw much light on the character of the interior sea which once occupied that basin.

7. Statistics of Coal, including Mineral Bituminous Substances employed in Arts and Manufactures; with their Geographical, Geological and Commercial Distribution, and amount of Production and Consumption on the American Continent, with Incidental Statistics of the Iron Manufacture, by R. C. TAYLOR, F.G.S. London, etc., etc. 2nd edition. Revised and brought down to 1854, by S. S. HALDEMAN, Prof. Nat. Sci. and Agric. in Delaware College, &c. 640 pp. 8vo, with maps, plates, and numerous wood-cuts. Philadelphia, 1845: J. W. Moore.-The first edition of this work was issued in 1848. Since that time the able