The feldspars of the above trachytes and phonolite offer some considerable variations in their composition, especially in the proportions of the alkalies. In IX, the proportions of potash and soda are nearly the same as in the trachytes of Brome, Shefford, and Chambly, and the same is true of XII. These are doubtless to be regarded as varieties of orthoclase with a large amount of soda, while in the feldspar from the phonolite the proportion of soda is very small. In x, on the contrary, the large predominance of soda indicates a composition approaching that of albite. It is further apparent, from a comparison of the feldspars of the other trachytes whose complete analyses are not given, that the proportions of the alkalies are liable to considerable variation, even in adjacent and apparently similar dikes. All of the above feldspars are probably to be referred to orthoclase, or to albite; but these, in the earthy trachytes, have undergone a commencement of decomposition, which consists in the loss of a portion of silica and alkali, and the combination of water, resulting in the formation of kaolin. An admixture of this substance will explain the increased amount of alumina, the deficiency of silica, and the presence of water in the feldspars of the more earthy of these trachytes.

These trachytic dikes are not confined to the vicinity of Montreal. To the southward, on the shores of Lake Champlain, there is found in and about Burlington, Vermont, a vast number of dikes of intrusive rock; some of which appear to intersect the strata of the Quebec group, and others those of the Trenton group. Some of these are described as being of greenstone; and others, as a white or yellowish-white feldspathic rock, often porphyritic from the presence of feldspar crystals. The base of a yellowish-gray porphyritic dike from Shelburne, having a rough fracture, and a specific gravity of 2.60, gave to Prof. G. F. Barker, silica 67.30, alumina and peroxyd of iron 19.10, lime 0.79, magnesia, traces, potash 474, soda 6 04, volatile 170 = 99-67. It contained a little intermingled quartz; and the mass resulting from the fusion of the rock with an alkaline carbonate, afforded traces of a sulphuret. (Geology of Vermont, pp. 579-707.)

=

Somewhat to the south of Burlington, on the west side of Lake Champlain, and near to Essex, there is a great mass of intrusive rock, found in the slates of the Hudson River formation. As described by Emmons, it is interstratified in an irregular manner among the layers of the unaltered sedimentary rocks,

and has a fissile and schistose structure, which gives, at first sight, the aspect of stratification to what is undoubtedly an intrusive rock. When exposed to the action of the waves on the lake-shore, its structure appears to be columnar, and sometimes concretionary. This rock is described as composed of a reddish or pale leek-green compact feldspar, holding crystals of the same mineral. (Geology of New York, vol. ii, p. 84.) These intrusive feldspathic rocks on Lake Champlain resemble closely the trachytes of Montreal and Chambly,-with the latter of which, the trachyte of Shelburne, the only one of them which has been chemically examined, closely agrees in composition.

[To be continued.]

ART. XI.-On the so-called "Barrel-Quartz," of Nova Scotia; by B. SILLIMAN, Jr.'

ON Laidlaw's Hill, forming the eastern division of the Waverley Gold District, has been found, in great abundance, a peculiar variety of quartz-rock which has acquired a wide reputation under the name of barrel-quartz.

Mr. Phillips, of London, has thus described it:

"The most remarkable deposit of auriferous quartz hitherto found in Nova Scotia is undoubtedly that at Laidlaw's Farm. The principal workings are here situated near the summit of a hill composed of hard, metamorphic shales, where openings have been made, to the depth of four or five feet, upon a nearly horizontal bed of corrugated quartz of from eight to ten inches in thickness. This auriferous deposit is entirely different from anything I had before seen, and when laid open presents the appearance of trees or logs of wood laid together side by side, after the manner of an American corduroy road.

"From this circumstance the miners have applied the name of 'barrel-quartz' to the formation, which, in many cases, presents From a Report by B. SILLIMAN, Jr., on the Waverley Gold Mining Co., Boston,

1864.

an appearance not unlike a series of small casks laid together side by side and end to end.

"The rock covering this remarkable horizontal vein is exceedingly hard; but beneath it, for some little distance, it is softer and more fissile. The quartz is itself foliated parallel to the lines of curvature, and exhibits a tendency to break in accordance with these striæ.

"The headings, and particularly the upper surfaces of the corrugations, are generally covered by a thin bark-like coating of brown oxyd of iron, which is seen frequently to enclose numerous particles of coarse gold, and the quartz in the vicinity of this oxyd of iron is itself often highly auriferous."

The accompanying section, (fig. 1) which I have prepared from a sketch of the place as I saw it in December, will, together with the following perspective view of the opening, convey a clear idea of its peculiar structure.

Only the corrugations in the open part of the cut are visible; the extension of the vein to the right and left, in fig. 1, is ideal, the superincumbent mass covering it. I measured, however, the quartzite above, dipping to the right and left at a small angle, and I think no geologist would doubt that the crest of an anticlinal axis here comes to the surface and has escaped the denudation which has removed the top of the crest in most places. The corrugations, or folds, appear to be accounted for on the hypothesis of a lateral thrust producing the undulations. The perspective view (fig. 2) of this interesting locality was taken from a stereoscopic photograph, showing the appearance of the barrelquartz after the surface-rock (quartzite) had been removed, and before the miners had broken up the quartz layer for removal. The value of the barrel-quartz has been not so much from its large average yield of gold as from the comparative cheapness with which it has been mined. Thus it appears from the statements in the Chief Gold Commissioner's Report, dated Jan., 1863, that each miner on Laidlaw's Farm averaged for the last three months of the previous year over nine tons per month, while in other districts the average monthly product per man was from two to three tons. The average yield of gold was small,--about five pennyweights to the ton; the maximum being three ounces, not including remarkable discoveries, like that of the Chebucto Company, of a mass of this quartz, yielding, as already mentioned in the Introduction, for a volume of not over two cubic feet, over $4000 in value, of gold.

SCIENTIFIC INTELLIGENCE.

I. PHYSICS AND CHEMISTRY.

1. On the constitution of the Sun.-MAGNUS has communicated a brief note in which he endeavors to show that purely thermic relations permit us to draw important inferences as to the physical character of the sun. If we observe the quantity of heat which is radiated from a non-luminous gas flame and then introduce soda into the flame, the quantity of heat radiated will be increased. The experiment was made in such a manner that a definite portion of the soda flame was constantly compared with the same part of the non-luminous flame, but so that the soda introduced into the flame could not radiate directly toward the thermoelectric pile. Although the temperature of the flame was lowered by the introduction of the soda, yet one-third more heat was radiated. When a plate of platinum was introduced into the flame instead of the soda, the quantity of heat radiated was much greater than before, although the plate absorbed more heat from the flame than the soda. With the plate of platinum employed, which was 55 millimetres broad, the amount of heat radiated was nearly twice as great as that of

the non-luminous flame. Variations in the thickness of the plates of platinum employed made no sensible difference in the heat radiated, provided that the plates had the same diameter. When the plate of plati num was covered with carbonate of soda, the radiation increased in a remarkable degree, being one-half greater than that of the plate alone. The quantity of heat radiated was still further increased when, in addition to the covered platinum plate, the flame contained soda vapor arising from a little soda placed below the plate in the flame and not itself radiating heat to the pile. Under these circumstances the covered plate radiated nearly three times as much heat as the flame alone. Salts of strontium and lithium behaved like salts of sodium. These experiments show that gaseous bodies radiate very much less heat than solids or liquids, and that consequently it can scarcely be assumed, that the gaseous photosphere of the sun is the source of the sun's heat. They show also that ignited soda at the same temperature has a much higher radiating power than ignited platinum. Finally, they prove that soda vapors absorb very little of the heat which is radiated by the solid or fluid ignited body, for the radiation of the solid body in the flame filled with the vapor of soda was but little less than the sum of the radiation of the solid alone and the vapor alone. This behavior of ignited soda in the fluid and gaseous condition, confirms the views of Kirchhoff on the constitution of the sun in a very striking manner.-Pogg. Ann., cxxi, 510.

W. G.

2. On the Spectrum of Thallium.-W. A. MILLER has found that when pieces of thallium are made to form the electrodes of an induction coil, the spark exhibits in the spectroscope five new lines in addition to the well known characteristic green line. The new lines are a very feeble line in the orange, two almost equally intense in the green and more refrangible than Tla, a third and weaker line in the green, and finally a bright sharp line in the blue. All these lines could be observed in an atmosphere of hydrogen, excepting the weakest, but they were in this case less intense. The photographed thallium spectrum exhibits a very characteristic group of lines resembling the spectra of cadmium and zinc, and somewhat less that of lead.-Phil. Mag., xxvi, 223.

W. G.

3. On the photographic transparency of various bodies, and on the photographic effects of metallic and other spectra obtained by means of the electric spark.-W. A. MILLER has published an interesting paper upon photographic transparency and kindred subjects, from which we extract the principal results only, referring for details to the original memoir. The author employed prisms, lenses, and plates of rock crystal to avoid the effect of absorption due to the use of glass. It was found that— (1.) Colorless bodies which possess equal powers of transmitting the luminous rays vary greatly in permeability to the chemical rays.

(2) Diactinic solids (that is to say, solids which are permeable to the chemical rays) preserve their diactinic power both when liquefied and when converted into vapor.

(3.) Colorless solids which are transparent to light, but which exert a considerable absorptive effect upon the chemical rays, preserve their absorptive power with greater or less intensity both in the liquid and the gaseous state.

These conclusions are equally true as regards liquids, whether the