engraved a square, ab; a crystal is seen upon it secured with wax, ab; at its centre is seen the orifice for the passage of the light, its size corresponding to that of the crystal to be examined: at some point on the edge is made a notch, which is adapted to a pin secured to the inside of the tube so that the position of the diaphragm shall remain fixed. By these means, the crystal under examination may be properly adjusted; two sides of the engraved square must coincide with the axis of the analyzing tourmaline, while two are at right angles with it. The movable cylinder carries an index, fig. 1, z, which traverses the graduations of the graduated semicircle. If now a cleavage plate of calcite be so fixed upon the diaphragm that a b' is parallel with a b of the engraved square as in fig. 3, and the movable cylinder be adjusted to zero, then a b' is also parallel with the longitudinal axis of the tourmaline, and no black cross is visible. The cylinder must now be turned until the cross appears normal, and the angle of revolution may be read off on the graduation. I have investigated various crystals in this manner, and have arrived at the following results which in general characterize the systems of crystallization. HEXAGONAL SYSTEM.-Through parallel planes of the hexagonal pyramid, the vertical arm of the black cross is seen at right angles to the basal edge (edge Z). Through parallel planes of the rhombohedron the cross arranges itself in the direction of the diagonals. Through the planes of the prism, the vertical arm of the black cross stands in the direction of the principle axis. Examples, quartz, calcite, beryl, soda nitre, corundum, apatite. Seen through the basal planes, the cross is not changed by a revolution of the cylinder. (Tourmaline has peculiarities, the account of which is here omitted.) DIMETRIC SYSTEM.-Through parallel planes of the square pyramid, the same relation was observed as in the hexagonal system: the same is true also for the planes of the prism, and the basal planes. When the edges of the pyramid are laid horizontal the cross appears revolved. Ex. meionite, vesuvian, apophyllite, zircon, mellite, chalcolite, rutile, etc. TRIMETRIC SYSTEM.-Seen through two parallel planes of the rhombic pyramid the normal arm of the cross is not at right angles with the basal edge. Ex. sulphate of zinc, of magnesia, and of nickel, topaz,* &c. Seen through the basal planes of the rhombic prism, the cross takes the direction of the diagonals. Ex. epsomite, topaz, muscovite, aragonite, barytes, &c. Through the lateral faces of the vertical rhombic and rectangular prisms, the cross stands in the direction of the vertical axis. Ex. anhydrite, &c. Through the faces of the domes, the normal arm of the cross is at right angles with the terminal edge of the dome. Ex. epsomite, &c. MONOCLINIC SYSTEM.--Through the oblique terminal planes the cross stands in the direction of the diagonals. Through the lateral planes * In general the angle of revolution upon the triangles of the pyramids of the dimetric and hexagonal systems are of two kinds, but in case of the trimetric system of three kinds, of the prism the cross does not stand in the direction of the principal axis and the system is thus distinguished from the Trimetric. Through the orthodiagonal planes the cross stands in the direction of the principal axis. Through the clinodiagonal planes it is not in the direction of the principal axis. These planes comport themselves very different from the similar ones in the rhombic system. Through the clinodiagonal domes the cross also appears revolved. Ex. orthoclase, augite, cane sugar, gypsum, borax, bicarbonate of potash, glauber salt, euclase. TRICLINIC SYSTEM.-The cross is oblique upon all planes, if an edge of the prism be placed parallel with the axis of the tourmaline. Ex., kyanite, bichromate of potash. Boracite is plainly doubly refractive. Yellow prussiate of potash is optically binaxial. Prof. von Kobell describes peculiarities in several species, which are here omitted. II. MINERALOGY AND GEOLOGY. 1. Mineralogical Notes; by T. S. HUNT.-Pyrrhotine. This species with the formula Fe, S., is regarded by Laurent as a protosulphuret in which a portion of iron exists as ferricum, (fe) with two-thirds its ordinary equivalent; the formula of the mineral is then (Fe, feg) S、 According to Schaffgotsch, some varieties have the composition Fe S, FenS3=Fes S4 or (Fe feg) S4, corresponding to magnetite Fe3O4 or (Fe fes)04. By thus regarding it as a protosulphuret, its relation to Greenockite is more apparent. Wilsonite.-The further examination of specimens of the mineral Wilsonite in the possession of Prof. E. J. Chapman has shown him that the form of this mineral is triclinic with inclination to the right. He gives as approximations the following angles obtained by the common goniometer with cleavage surfaces. P: T 94°; P: e = 145°; Te = 129°; P: M and T: M = 110° to 115°. Cleavage perfect with P and T, less so with M. The cleavage with e, according to Chapman, "is not easily obtained, but is very distinct and even. Density 2.77. Hardness 35 cn the more facile cleavages, and their combination edges; 55 on the ends of the prismatic concretions.” Prof. Chapman also pointed out to me the existence of intermingled carbonate of lime in the specimens which I had previously analyzed, and I have since found that the finely pulverized mineral yields up almost the whole of its lime to cold dilute hydrochloric acid, which does not attack the silicate. This still retains its rose color, and is a hydrous silicate of alumina and potash, with a little magnesia. The results of the analyis by myself of two specimens thus purified, (1 and 2,) and a partial analysis kindly furnished me by Prof. Croft, of a third, are as follows: I JJ. The pure mineral from which the carbonate of lime has been removed, seems to be uniform in composition, and approaches the feldspars in constitution. Bytownite.-Bytownite I suppose to be anorthite with some quartz, or more probably a mixture of different feldspars. It is very similar in composition to Genth's thiorsauite. All those triclinic feldspars intermediate in composition between anorthite and albite, appear to be only crystalline mixtures of these two species. See Am. Jour. of Science, [2], xviii, 270. Magnesite.-A silicious magnesite rock of considerable extent is found among the strata of the Hudson River group in Bolton, Lower Canada. Its analysis gave carbonate of magnesia, 60 13, carbonate of iron 8:32, silica with a little chromic oxyd 32-20=100 65. The serpentines of this formation are believed to result from the alteration of this silicious carbonate, in the presence of water. (See Geol. Rep. Canada.) Dolomite-A very compact, fine grained coral limestone from the Island of Matea, north of Tahiti, furnished me by Mr. Dana from the Collections of the U. S. Expl. Expedition, has a hardness greater than fluor; and a density in powder, equal to 2-830. Its analysis gave Carbonate of lime 60 50, carbonate of magnesia 38.77, silica, etc., 0·30= 99.57. Another determination gave 38 25 of carbonate of magnesia. [This analysis confirms the result of Prof. Silliman, Jr., (this Jour., [2], xiv, 82) and shows that the dolomisation took place in the consolidation of the coral material. The rock is the white compact limestone of Matea, an elevated coral island, and resembles much of the rock found about other reefs. It is as solid and firm as any Silurian limestone. See the writer's Geol. Report, and also this Jour., xiv, 76.-J. D. D.] 2. Notice of a new Locality of Molybdate of Iron? by WM. J. TAYLOR.-I obtained in September last a mineral from Heard County, Georgia, which resembles in every respect the molybdate of iron, recently described by D. D. Owen, (Proc. Ac. Nat. Sci. Philad., vi, 108), from the gold region, near Nevada city, California. It consists of deep yellow, silky tufts, formed by groups of delicate, acicular crystals, coating and filling the cavities of dark ferruginous quartz. This quartz forms numerous veins in micaceous and granitic rocks, in a district where gold has been found. A qualitative analysis showed Mo, Fe. It has been as yet impossible to obtain sufficient of the mineral for a thorough quantitative analysis. 3. Reaction of common salt in the formation of Minerals; M. FORCHHAMMER.--On fusing together phosphate of lime (the phosphate of bones) and chlorid of sodium (four parts to one of the phosphate) he obtained after a slow cooling a mass in which were many cavities covered with prismatic hexagonal crystals, which were apatite in composition; the specific gravity 3-069. At the temperature of fusing, apatite dissolves readily in common salt and separates in needle-form crystals. By this method small quantities of phosphoric acid in rocks may be detected; they are to be melted with 50 to 100 parts of common salt, and if easily fusible the silicates separate easily from the salt; if not, chlorid of sodium fills the cavities in the vesicular mass, resembling the cavities in an amygdaloid. M. Forchhammer concludes that common salt has played an important part in the formation of minerals.-Pogg. Ann., xci, 568. 4. Gneiss.-Analyses by F. Schönfeld and H. E. Roscoe, (Ann. Ch. u. Pharm., xci, 302.)-1, a mica slate from the right shore of the Eisack G. 31410; 2, gneiss from Cachoeria da Campo, Brazil, consisting of orthoclase, quartz, and mica, yellowish-gray in color, G.-2.6128; 3, so-called protogine, from the north side of Mont Blanc, a hundred feet below the highest peak, G. 2.7088; 4, gneiss from Norberg, Sweden, consisting of flesh-colored orthoclase, quartz, and grayish-black mica; 5, ibid., a fine grained mixture of orthoclase and quartz. ΕΙ Fe Ča Mg K Na H Si 1. Mica slate, 69:45 14.24 67.32 16:08 6.54 2.66 1.35 2.52 4:02 0.52 101.30 3.87 1.54 2.58 2.49 -=101-10 101.17 5. Meteoric Iron from Greenland.-Forchhammer describes this mass as weighing 21 pounds; it is 7 inches long, 7 high and 5 broad. Specific gravity 7.00-7.02, Rinck. Hardness like that of steel. With nitric acid affords fine Widmanstättian figures. Composition (Pogg. Ann., xciii, 155) Fe 93 39 Ni 1:56 Co 0.25 Cu 0:45 S 0-67 Ph 0.18 C 1.69 Si 0-38-98-57 The large proportion of carbon is peculiar. 6. On the Sandstone and Coal of North Carolina of the age of the Richmond coal basin; by Prof. D. OLMSTED.*-[The following observations are from the Geological Report on North Carolina, by Prof. D. Olmsted, published in 1824, the first of all the State Geological Reports, made in this country. The facts have not appeared in this Journal, and as the Report was long since out of print, we republish them. The author, at the time when the investigations were made, was Professor of Chemistry and Mineralogy in the Universtity of North Carolina.] Freestone and Coal formation of Orange and Chatham." The formation is very extensive, embracing a great number of beds of excellent freestone, varying among themselves in color and texture, but nearly all extremely well suited to the purposes of architecture. The sandstone extends from Oxford in a southerly direction, quite through the State. Its length, within our own State, is about 120 miles. The breadth of the formation varies considerably in different places. On the southeast of Oxford it disappears among the valleys, converging almost to a point; on the Neuse, its breadth is about 12 miles; between Raleigh and Chapel Hill, it is 18 miles; not more than 8 miles on the Cape Fear, but southward of that, it grows a little wider. Its average breadth may therefore be stated at about 12 miles. On this supposition, the whole area of the formation is 1440 miles. In going from Oxford to Chapel Hill, the traveller passes nearly on the line of its western boundary. This runs onward, at the foot of Chapel Hill, a mile and a half east of the University; meets Haw River about three miles above Haywood, and Deep River five miles northwest of Tyson's Mills. Thence it passes through Moore County, by Richland Creek; thence * Professor Olmsted's first announcement of these coal mines will be found in this Journal, ii, 175, 1820, and v, 228, 1822. An abstract of a paper on these mines by Professor W. R. Johnston is contained in Proc. Amer. Assoc., iv, 274, New Haven meeting, 1850, |