SYRACUSE

144

The American Naturalist.

[February,

careful and conscientious manner. -Wyrouboff,15 in a reply to Martin's article, states that the latter's results differ but little from his own, and that the conclusions reached by him comprehend no new notions. -The writer last referred to (W.) has recently 16 completed a series of experiments on circularly polarizing substances, by which he seems to have shown that the peculiar property of these bodies is due to their structure, which is described by Mallard as an irregular piling of very small biaxial plates. In this way a high grade of symmetry is imitated, while the plates are really of a low grade. He also adds a nineteenth substance to the list of rotatory polarizing bodies, viz., (NH)LiSO, which is apparently biaxial and positive.The effect of temperature upon the optical and crystallographic constants of prismatic sulphur has been thorougly investigated by Schrauf, who records his results in an excellent paper of fifty-nine pages. The first part discusses the values of the interfacial angles at different temperatures. The second is confined to refractive phenomena, such as the refractive index for different wave lengths. The third and fourth contain calculations of the values of the optical constants, and the fifth contains a discussion of the relations existing between the refractive indices and the wave length of the transmitted light, temperature, and other factors, and concludes with remarks on the constancy of the refractive and dispersive power, and upon the crystal form of prismatic sulphur.A paper by Becke 18 on the etching of fluorite is a remarkable exhibit of careful and painstaking work in this branch of physical mineralogy. The author has subjected both natural and prepared faces of crystals from various localities to the action of acids and alkalies of various strengths and at different temperatures, and has studied the results produced. The symmetry of the figures obtained indicate a tetragonal symmetry for the mineral. Anomalous figures on some crystals, found only on planes that show double refraction, are explained as due to the manner of growth. Many new ideas are gathered from the study, one of the most important of which is embodied in a restatement of the law of symmetry of etched figures. These possess the symmetry of the face on which they occur only when this is a natural one free from striations, vicinal planes, etc. Experiments on the solubility of the mineral in different directions lead to the expression of a law of solubility as follows: The rapidity of solubility is equal along equivalent crystallo

15 Bull. Soc. Franc. d. Min., XIII., 1890, p. 94.

16 Ib., p. 215.

17 Zeits. f. Kryst., XVIII., 1890, p. 114.

18 Miner. u. Petrog. Mitth., XI., 1890, p. 349.

graphic directions, and different along unequivalent directions. Further, the author finds that elevations due to etching (aetzhügel) occur on faces least capable of resisting solution, while depressions (aetzgrübchen) are produced in the least soluble faces. Etching zones, he defines as those containing the planes with the greatest capacity for resisting solution. Many more results of interest are contained in the paper, the character of which is sufficiently indicated by the conclusions above referred to. The natural etched figures on the topaz of San Louis Potosi, Mexico, correspond in symmetry with the faces on which they occur, with the exception of those on the brachypinacoid 2P, which are unsymmetrical. According to Pelikan 19 they resemble the figures produced by Baumhauer upon treating the mineral with molten potassa.Dufet 20 obtains 1.54421 as the value of the refractive index of quartz, based on the examination of seventeen different specimens of the mineral.

Miscellaneous.-The cosmic dust (kryokonite) collected by Nordenskjöld in Greenland, in 1883, has been submitted to Wülfing 21 for investigation, by whom it has been found to consist in greater part of feldspar, quartz, mica, and hornblende. There are present in it also garnet, zircon, magnetite, augite, and sillimanite, and with them is mixed a nitrogenous organic substance. The most interesting constituents of the dust are little chondri of opaque, isotropic transparent, and double refractive material. The larger part of the dust is thought to be a sediment from the air, and to have been obtained by it from a region of crystalline schists. The chondri, on the other hand, are thought to be of cosmic origin, since they are similar to the chondri obtained in deep-sea soundings. If the amount of the dust collected from the snow in Greenland represents the fall of one year, the total amount falling upon the entire surface of the earth in this time is 125 million kilograms, equivalent to a cube of thirty-one yards on a side.A new crystal refractometer has been devised by Czapski. 22 Its construction and use is carefully described by the inventor in a recent paper in the Neues Jahrbuch.—That a definite relation exists between the habits of crystals of certain minerals and their mode of formation has long been recognized, but it has been left for Arzruni 23 to undertake a systematic study of this relation.

19 Ib., XI., 1890, p. 331.

20 Bull. Soc. Franc. d. Min., XIII., 1890, p. 271. 21 Neues Jahrb. f. Min., etc., B. B., VII., p. 152.

22 Neues Jahrb. f. Min., etc., B. B., VII., p. 175. 23 Zeits. f. Kryst., XVIII., 1890, p. 44.

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late paper this writer communicates the results of the examination of crystals of hematite produced by sublimation in smelting furnaces and those from San Sebastiano, Italy, that are supposed to have been formed in an analogous manner. In all of these the habit is the same, although different combinations of nearly related forms occur on them. Sublimed valentinite and senarmontite are likewise studied. Cuprite produced by slow oxidation at a low temperature has an octahedral or dodecahedral habit, while that produced at a high temperature is probably hexahedral. Struvite obtained from a solution of Koch's peptone differs materially from the natural mineral, but the differences have not yet been carefully enough studied to warrant any general conclusion being drawn from the observations. Further articles from Prof. Arzruni will be looked for with interest..

MINERALOGY AND PETROGRAPHY.1

Petrographical News.-The protogine of Mont Blanc is shown by Lévy to be a true eruptive, apophyses from which penetrate the surrounding schists and alter them, and break from them fragments which they hold as inclusions. These fragments have been regarded as basic segregations, and the surrounding schists have been looked upon as dynamo-metamorphosed phases of the protogine. Both of these views the author combats. Among the schists he finds eclogites, with diopside in micropegmatitic intergrowths with quartz and feldspar, amphibolites and mica-schists, each of which classes is briefly described. The segregations mentioned occur most frequently near the contact of the granite with the schists. Many of them resemble so closely certain phases of the schists that Lévy is compelled to regard them as fragments of these caught up by the eruptive during its passage from below. A microgranite from the periphery of the main mass of granite consists of corroded crystals of the first generation cemented by a granitic ground-mass. This fact is thought to be an indication of the correctness of the view that the constituents of granite are mainly of the second generation, those of the first consolidation having disappeared. To the southeast of Mont Blanc are quartz-porphyries which, according to Graeff,3 are genetically related to the granite composing the body of the mountain. Like the latter, the porphyries have been subjected to pressure, by which process much sericite has been developed, resulting in sericite-schists. The present contact of the eruptives with the gneisses and mica-schists of the Mont Blanc "massif is thought not to be an original contact, but one brought about by dislocations. The conclusions of Lévy and Graeff are thus seen to be in accord in some particulars, while in others they are at variance. Fuller discussions are promised later.In the first part of a general 1 Edited by Dr. W. S. Bayley, Colby University, Waterville, Me.

2 Bull. des Serv. d. 1. Carte. gèol. d. la France, No. 9, 1890.

Archiv. des Sciences phys. et nat., Nov., 1890.

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