(EXTRACTED FROM THE AMERICAN NATURAList, May, 1887.) MINERALOGY AND PETROGRAPHY.' Petrographical News.-A few specimens of basic eruptive rocks have recently been described by Schmidt from the north side of the Central Alps in Switzerland. Near Iberg, in Canton Schwyz, a diabase porphyrite occurs cutting Eocene deposits. This porphyrite presents all the characteristics of pre-Tertiary porphyrites. It offers another proof of the fact that texture in rocks depends more upon the conditions under which the rock magma solidified than upon the age during which it was erupted. The porphyritic crystals are oligoclase. Many of them consist merely of an outer shell of plagioclase substance, including material identical with that of the ground-mass. Melaphyres from near Glarus contain olivine crystals, which have undergone the unusual alteration into bastite.Messrs. Barrois and Offret 3 have found that the rocks of the Sierra Nevada Mountains in Southern Spain are similar in many respects to those of the Ronda Mountains. They consist principally of a series of highly-altered schists and limestones. The mica schists of this series contain in addition to their essential constituents the accessory minerals rutile, tourmaline, garnet, muscovite, kyanite, sillimanite, andalusite, and occasionally feldspar. Garnet and staurolite are among the oldest constituents. Their shattered condition shows that the rock in which they occur has been subjected to great pressure. The Cambrian schists of this region are divided into sericite schists and chloritoid schists. Members of both series are cut by veins of quartz, with which are associated fluorine minerals, a fact which leads the authors to regard these as the products of the action of gaseous emanations upon the material of the surrounding rock-masses. Among the Cambrian amphibolites is mentioned a variety containing glaucophane, with a greenishblue tint instead of a violet-blue color parallel to b. The composition of this glaucophane is: -A dyke of diabase cutting the old red sandstone near Dumbarton, Scotland, is described by Lacroix5 as presenting a fine example of the existence in the same rock-mass of three distinct types of structure, the devitrified glassy, the porphyritic, and the ophitic.The analyses of several rocks from the neighborhood of Christiania, Norway, have recently been published." The rocks analyzed are, with one exception, from the area occuEdited by Dr. W. S. BAYLEY, Madison, Wisconsin. 2 Neues Jahrb. f. Min., etc., 1887, i. p. 58. 3 Comptes Rendus, ciii., 1886, pp. 174 and 221. 5 Comptes Rendus, ciii., 1886, p. 824. pied by the prädacite of Lang, and its contact zone. By comparison of the composition of an unaltered slate with that of a hornfels produced by its alteration, it is seen that in this process water and carbon dioxide were driven off, and the ferric iron in the former was reduced to the ferrous state in the latter. The brown mica of the hornfels contains 3.40 per cent. of titanic oxide. Fulgurites. Although the interesting bodies known as lightning-tubes have been the subjects of numerous papers during the past century, it must be confessed that our knowledge in regard to them is not very extensive. The United States National Museum having recently become possessed of several fine specimens of the tubular varieties formed by lightning striking in loose sand, Mr. G. P. Merrill' has been enabled to study these microscopically, and thus to add something to our previous knowledge of them. In all the cases examined the walls of the tubes consisted of glass, in which there were no traces of crystallization. Analyses of the glass and of the sand in which the fulgurites are found and by the fusion of which they were produced, show that in every case the former contains more silica than the latter. The author argues that "had the lightning shown no selective power the resultant glass would possess the same composition as the sand in which it formed. Had it exercised such power one would naturally expect the most fusible minerals to be first acted on, and hence that the glass would approach them in composition." But the contrary of this seems to have taken place, the ordinarily infusible quartz having been most acted upon. This may probably be explained by supposing the quartz to offer the greatest resistance to the passage of the electric current, -i.e., to be a very poor conductor of electricity. It would then in consequence of this resistance become heated even to the point of fusion, while the better conductors would escape with little injury. The resulting glass would in this case have a higher percentage of silica than the surrounding sand. The actual composition of glass and sand from Union Grove, Whitesides County, Ill., yielded Professor Clarke: Loss on ignition SiO, Fe,O,. AlО, CaO MgO K,0 Na,O Fulgurite glass.......... 0.33 The 1.01 0.38 0.12 0.73 0.77 1.16 0.13 1.13 1.50 paper concludes with a very full bibliography of the subject. 2 Mineralogical News.-A variety of the rare mineral carphosiderite is described by Lacroix from the triassic arkoses of Macon (Saône-et-Loire). It occurs as micaceous coatings of a 2 Proceedings of United States National Museum, 1886, p. 83. golden-yellow color on the walls of cavities and cracks. Examined microscopically, it is seen to consist of pleochroic (colorless and pale yellow) needles in a light yellow non-pleochroic ground-mass. Under crossed nicols the former show bright polarization colors, while the latter remains unchanged during a complete revolution, and is therefore regarded as being made up of the same acicular crystals cut perpendicular to their optical axes, which are negative. The specific gravity of the mineral is 3.09. It is infusible, and when heated in a glass tube gives off water and sulphuric acid. Its composition is: SO, 30.18, P20,= 2.72, Fe,O, = 48.52, H,O= 18.48. -In the same journal Gonnard' describes pleromorphs of quartz after fluorite. Curious blocks of milky quartz from St. Clement (Puy de Dôme) are seen, upon close examination, to be made up of spherules composed of acicular crystals of quartz radially arranged around a centre, which is sometimes a void, but more frequently a piece of granite or a core of amorphous silica. Scattered through the blocks are found cavities of octahedral form, normal to the faces of which the quartz-fibres are arranged. Inside of the cavities are also occasionally little octahedrons of quartz with their faces parallel to the walls of the cavity. Several doubtful minerals have recently been examined microscopically by Dr. Lacroix. Pterolite, which Dana supposed to be an altered lepidomelane, Lacroix found to be a mixture of several distinct minerals, of which the most important are a black mica and a strongly pleochroic pyroxene. In addition to these there are also present in pterolite numerous grains of blue sodalite, rhombohedra of calcite or dolomite, and many other minerals which are usually found in eleolite syenites. Villarsite is shown to be merely a pseudomorph of chrysotile after olivine. Gamsigradite has the optical properties of hornblende, with a maximum extinction of 30° and pleochroism in green and brown tints.In a late number of the Neues Jahrbuch für Mineralogie F. Sandberger 3 discusses the widespread occurrence of iodine in phosphorites, of lithium in psilomelane, and of cassiterite and anatase crystals in zinc-blende and in tetrahedrite. He also describes hexagonal plates of kaolin, which he thinks are orthorhombic crystals bounded by the planes OP, ∞ P∞ and ∞P. They are found in the clefts and druses of a quartz vein occurring on the contact between a lithium-mica granite and a mica schist at the Morgenstern Mine, Joachimsthal. -In connection with his work on mineral veins the same author had occasion to examine the mica of the Schapbach gneisses and the augite of a diabase from near Andreasberg, Harz. In each he found a silver content of about 0.001 per 2 Ib., civ., 1887, p. 97. 4 Ib., p. 111. * Comptes Rendus, ciii., 1886, p. 1036. cent. The crystals of phenacite occurring at various localities in Colorado, according to Mr. Penfield,' possess a great similarity of habit to those from the Ilmengebirge, Urals. The phenacite from the Pike's Peak region (as well as the amazon stone and smoky quartz from the same locality) is found in pockets in the neighborhood of the Crystal Peaks," a chain of granite hills about fifteen to twenty miles northwest of Pike's Peak. The crystals from this place are usually small in size, the largest ever found measuring but 15 mm. in length. Most of the crystals are colorless, but those entirely imbedded in gangue have a faint wine color.Mr. A. N. Alling 3 has recalculated the physical constants for topaz from measurements of a crystal of this mineral from Thomas Range, Utah. The axial ratio as recalculated is a: b: c' 0.5285: 1:0.47715. The optical angle, 2 V = 67° 18'; and the indices of refraction are ẞ= 1.6104 andy 1.6176 for yellow light. = = Chemical Integration. The author regards all chemical species known to us as units or integers produced by the identification in volume, or, in other words, the integration of more elemental species. Rejecting the atomic hypothesis which he has long regarded as, in the language of J. P. Cooke, "a temporary expedient for representing the facts of chemistry to the mind," the author designates the so-called molecular weights of species as their integral weights. They are, at the same time, equivalent weights, since they are the weights of equal volumes. The specific gravity at o° and 760 mm. of hydrogen gas, which is the unit of combining weight, should, in his opinion, be made the unit of specific gravity for all species. The integral weights for gases and vapors are well known to be multiples of this unit of specific gravity, and, believing the law of condensation by volume to be universal, the author conceives all liquid and solid species to be formed by the condensation or so-called polymenzation of normal gaseous species often unknown to us. From this he concludes that the specific gravity of these liquids and solids should be calculated on the basis of hydrogen as unity. In this way the problem of the coefficient of condensation is solved. We had long maintained that the law of progressive series is also, like that of volumes, universal in chemistry, applying not only to related hydrocarbons, but to species differing in the proportions of oxygen, of sulphur, of metals, and of hydrogen. In the existence of such series he finds an explanation of those apparent variations in the law of definite proportions, seen alike 1 Amer. Jour. Sci., xxxii., Feb. 1887, p. 130. 3 Ib., xxiii., Feb. 1887. |