not a single tree or blade of green grass was distinguishable for nearly 30 miles, the ground being covered with a very prickly plant, to which we gave the name of whins. This shrub was almost black, seeming as if burnt, and the leaves were so much parched from the arid wind of Tartary, that they might be ground to powder by rubbing them between the hands. The brownish tint of the whins, together with the bleakness of the country, have the appearance of an extensive heath, and must ́strongly remind a Highlander of his native land. Our course from Brooang Pass was about NE.; here we found we had reached the northernmost point of the Sutluj, in Lat. 31° 50′. It lay about two miles on our left hand; and from this place, its direction, all the way to its source in the famous Lake of Mansuwurer, is nearly ESE. The wind was so strong that we could with difficulty keep our feet; and it is said to blow with almost equal violence throughout the year. We saw some snow on our right, a little below us; and beyond it, a peak, above 20,000 feet high, from which the snow was drifting in showers by the force of the wind. From the pass to camp, the road was a moderate descent upon gravel, winding very much. Shipke is a large village, in the small district of Rong-zhoong, under the Deba or Governor of Chubrung, a town, or rather a collection of tents, on the left bank of the Sutluj, eight marches to the eastward. The houses here, which are very much scattered, are built of stone, and flat-roofed; there are gardens before each, hedged with gooseberries, which give them a neat appearance. This is a populous place. We counted upwards of 80 men, who, on our arrival, came to meet us, being the first Europeans they had ever seen. The Tartars pleased us much; they have none of that ferocity of character so commonly ascribed to them; they have something of the Chinese features, and their eyes are small. They all go bare-headed even in the coldest weather, and have their hair plaited into a number of folds, ending in a tail, which reaches to their rumps. Their dress consists of a garment of blanket, trowsers of striped woollen stuff resembling tartan, and stockings or boots of red blanket, to which are sewed leather-shoes. Most of them wear necklaces, upon which are strung pieces of quartz or bone; they have also knives in brass or silver cases: all carry iron-pipes of the same shape as those used by labourers at home, and the higher classes have them generally ornamented with silver. In common with the inhabitants of Koonawur, the greater part of them have a flint and piece of steel for striking fire, attached to their apparel by a metal chain. The women, whose dress resembles that of the men, were literally groaning under a load of ornaments, which are mostly of iron or brass, inlaid with silver or tin, and beads round their necks, wrists, ancles, &c. and affixed to almost every part of their clothes. ART. XVIII.—A comparative View of the Series of Crystallisation of Epidote and of Glauber-Salt. By WILLIAM HAIDINGER, Esq. F. R. S. E. Communicated by the Author. VARIOUS Opinions have hitherto prevailed among mineralo gists relative to the question, whether several species with forms of variable dimensions, possess exactly the same form, or whether they all differ from each other in these respects. This however, is a matter which will probably remain unsettled for some time, although good authorities may be quoted in favour of either of the two different cases. With the exception of those minerals whose forms are comprised in the tessular system, the Abbé Haüy took for granted that every species would have its peculiar series, or, as he used to call it, its peculiar system of crystallisation. This very probable supposition found numerous adherents, and was generally received, when Professor Mitscherlich published his interesting labours on the isomorphous bodies, in which he asserted the perfect identity of the crystalline forms presented by several substances. The followers of a contrary opinion have brought forward instances, where the coincidence of the angles in two different species, containing isomorphous substances in the required proportions, does not take place rigorously; but many accurate observations shew, that at least the differences are sometimes very trifling. Thus, the isomorphous sulphates of zinc and of magnesia (Zn S2 + ces. 14 Aq and Mg S2+14 Aq) possess prismatic forms, the first dependent upon a scalene four-sided pyramid P=127° 27′; 126° 45'; 78° 5′, the other upon P=127° 22′; 126° 48′; 78° 7′: the forms of the two isomorphous species, of rhombohedral Corundum, and of rhombohedral Iron-ore (Äl and Fe) are derivable from acute rhombohedrons, the first from R-86° 6, the second from R-85° 58', &c. But, however striking this coincidence may be, as the differences may lie between the limits of errors of observation, yet there are many instances of isomorphous combinations, where the angles vary beyond these limits, and indicate that it would be too precipitate to assume a perfect equality even for the other. But it will not admit of a doubt, that there really are certain analogies in the forms of crystallisation among certain compounds of analogous substanThus, the carbonates of lime, of iron, of manganese, of zinc, of lime and iron, of lime and magnesia, and others, affect rhombohedral forms, and are cleavable parallel to the faces of a finite, obtuse rhombohedron of that system; on the other hand, the carbonates of lime, of lead, of barytes, of strontites, exhibit as remarkable analogies in the prismatic forms which they present, and which extend not only to the relative measures of their angles, and the occurrence of very nearly the same simple forms, but also to the peculiar mode of regular composition, so very frequently found in every one of these substances. If we abstract from the chemical relations, the analogies of the forms still remain, and their consideration becomes a pure crystallographic problem: it will even be necessary to carry the comparison farther than could be indicated by the chemical analysis, and include, for instance, in the comparative consideration of the above mentioned prismatic forms, also those of prismatic Iron-pyrites, of prismatic Melane-glance (brittle silver-ore), of prismatic Corundum (chrysoberyl), and others, which present very nearly the same peculiarities in their series of crystallisation. In the study of these analogies, though they have been observed by the earliest crystallographers, yet an extensive field is still open to the inquiry of naturalists, and cannot but yield highly interesting results, when carried on with the circumspection which it requires. There exists a very remarkable analogy of this kind between the crystalline forms of Epidote (prismatoidal Augite-spar) and of Hydrous Sulphate of Soda (prismatic Glauber-salt), as obtained from a recent and more accurate examination of these two substances, in the Treatise on Mineralogy by Professcr Mohs. The relations of the different simple forms occurring in the two species are almost identical, though the absolute measure of the angles of the one is considerably distant from that of the other. The crystals of Glauber-salt have been hitherto but imperfectly described. Haüy* ascribed to this species, on the authority of Romé de l'Isle, the form of a square prism, terminated by an isosceles four-sided pyramid, in which he has been followed by a great number of mineralogists. Count Bournon† states the primitive form of the substance to be an oblique-angular four-sided prism of 108o and 72° or nearly so. He came nearer the truth than Haüy, but did not yet establish the hemiprismatic character of the crystalline forms of the species. The history of the forms of Epidote is not so simple as that of Glauber-salt. Several varieties of the species itself had been formerly comprised under the general name of Schörl, and its forms were compared by Romé de l'Isle to those of Augite, a species which he considered to be nearly allied to Epidote, (paratomous Augite-spar), with this difference only, that the crystals of one of these substances were commonly elongated, and implanted in another direction than those of the other. Supported by his mathematical considerations of forms, Haüy, who first established Epidote into a particular species, gave another position to the crystals of this substance ‡ than that which he assigned to the forms of Augite §. He supposed the elongation of those crystals to take place in the direction of their principal axis, and gave for their primitive form a four-sided prism, of which the transverse section is a rhomboid of 114° 37′ and 65° 23; the sides of this prism are to each other in the ratio 110: 96; and its base is perpendicular to the lateral faces. The analogous position of both substances indicated by Romé de l'Isle, was no doubt preferable, and had Haüy adopted it, he *Tabl. Comp. p. 19. Traité, t. iii. p. 102. + Catalogue, p. 183. would have been able to render the description and figures of Epidote as clear and intelligible as those of Pyroxène or Amphibole. As they are, they shew more that their author was intimately acquainted with the subject he treats, than they are adapted to the use of the student. By a decrements of cone series of molecules along the acute vertical edge of the primitive form, this prism is changed into an irregular six-sided one, whose transverse section contains two angles of (114° 37′, two of 116° 40', and two of 128° 43'. The difference between the two first of these angles is expressed in the ratio of the sides of the primitive form, and has suggested to Hauy the name of Epidote. This observation is the more remarkable, as the instrument which Hauy employed requires the crystals to be very perfect, in order to perceive the small difference of about 2°. Epidote has been the subject of a particular and very elaborate memoir by Professor Weiss *, in which he re-establishes that analogous position of forms, in which Romé de l'Isle had endeavoured to compare them with the forms of Augite, with this difference, that Romé de l'Isle considered the crystals, of both substances, in that position which Haüy has chosen for epidote, while Weiss has placed them in that which has been given by Hauy to the crystals of pyroxène. This was a considerable step farther in their study, in order to find out analogies with the forms of other substances. Weiss, however, has not been fortunate in fixing upon that situation of the crystals which makes the faces r, Fig. 1. Plate X., vertical, or parallel to the principal axis, because in this situation the relations between the simple forms become unnecessarily complicated. Not having himself measured with care the crystals of this substance, he was forced to rely on the data of Hauy, But he referred theoretically the ratios among the different forms occurring in the species to that of three lines perpendicular to each other, and thus it happened that, although more intelligible and easy to be compared with other species, his mode of considering the forms of Epidote is less correct and applicable to nature than that of Hauy. In the position in which Professor Mohs considers the crystals of Epidote or prismatoidal Augite-spart, the faces M cor Abhandl. d. Akad, d. Wissensch, zu Berlin, for 1818 and 1819, p. 242. + Grundriss der Mineralogie, Th. i, p. 561. |