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the “Lower” and “Upper” Coal Measures do have a relation of one above the other and from a mining standpoint of an upper and a lower member, they do not hold positions indicating that as a whole the one is geologically older than the other, or that the lower was deposited before the upper. On the other hand, the facts show clearly that the terms lower and upper are misnomers in the sense that they are usually used, carrying with them as they do the idea of relative age. More. over, along the great bedding planes marginal sediments were laid down at the same time as thalassic deposits were formed farther out from the shore. Therefore, as a line for the separation of the Coal Measures into two subdivisions, into a productive and a barren series, as a line which under existing conditions is of practical use in mining operations, one which also indicates the first marked physical and faunal changes in the sequence of strata in passing in a seaward direction from the ancient margins of the basin, the first great limestone met with was selected as the most reasonable, natural and convenient horizon. For this reason, it was stated* that in considering the Coal Measures as a whole, two tolerably distinct classes of sediments were readily recognized : (1) the marginal or coastal deposits, and (2) the beds laid down in the more open sea. These two categories are sharply contrasted lithologically, stratigraphically and faunally.
The first category is characterized by the rocks being predominantly argillaceous shales and sandstones, with practically no limestones. The individual beds usually are very limited in extent, and replace one another in rapid succession, both laterally and vertically. The sandstones often form great lenticular masses, sometimes deeply channeled on the upper surface, the excavations being filled with Coal Measure clays. These and many other phenomena attest a constantly shifting shore line and shallow waters. The fossils contained are nearly all brackish water forms, or shore species. Remains of pelagic organisms are not numerous.
On the other hand, the second class of deposits is made up largely of calcareous shales, with heavy beds of limestone. The layers are evenly bedded, and extend over very considerable distances. The faunas are chiefly composed of strictly open-sea forms.
With this idea of the Coal Measures of the Interior basin, the limits of the two formations in Iowa and the districts to the south assume somewhat different lines from those which have been commonly recognized. The geological cross-sections recently made in central Iowa
* Missouri Geol. Sur., vol. iv, pp. 80-82; Jefferson City, 1894.
show clearly that the thick limestone of Winterset may be regarded as the base of the “Upper” Coal Measures. Coastal sediments carrying workable seams continue up to this line. Above it, open-sea deposits abruptly replace the former, and the coal veins are almost entirely wanting. This is admirably shown in the sections along Middle river in central Iowa, where Tilton* has gone into details on the subject. In one direction the course of the outcrop of the great limestone of Winterset is northwestward froin the typical locality. It passes from Madison county through Guthrie and soon is lost beneath the Cretaceous. In the opposite direction it has been traced southward to the southern boundary of Iowa. In Missouri it appears to be continued by what is known as the Bethany limestone, which sweeps southward and then southwestward in a broad arc into Kansas. At Kansas City it seems to be represented by one of the principal beds exposed in the bluffs at that place. In Kansas Hawortht has just announced that he has traced what he calls the Erie or Triple limestone across the state in a southwesterly direction from Kansas City into Oklahoma territory; and that he has correlated it with the Bethany limestone of Missouri. With the recognition of these facts the base of the Upper Coal Measures has been traced over all of the Western Interior coal basin.
The appellation Bethany limestone for the basal formation of the Upper Coal Measures may be extended somewhat, so as to include more than No. 78 of the Broadhead section in Missouri and may be made to cover several of the limestone beds above the layer to which the term Bethany Falls was originally applied, for the reason that these layers are sep. arated from the main bed only by thin, unimportant seams of shale. Thus it appears that the Winterset limestone of Iowa and the Erie limestone of Kansas are but extensions of the Bethany limestone of Missouri as now understood ; and as the latter was the first to be recognized and to receive a specific geographical name, it has priority and must therefore supplant the other terms proposed.
* lowa Geol. Sur., ii, pp. 135-146; Des Moines, 1895. + Kansas Univ. Quart., vol. ini, pp. 293; Lawrence, 1895.
ART. XXIV.-On the so-called Schneebergite; by A. S.
EAKLE and W. MUTHMAN.
IN the year 1880, A. Brezina* published a short announcement, “ Ueber ein neues mineral, den Schneebergit," which was found on the Bockleitner Halde at Schneeberg in Tyrol. A qualitative analysis by H. Weidel gave as the principal constituents antimony and calcium, so Brezina supposed it might be a second modification of romeite or roineine, which according to Dainour should have the formula Sb,0,. Sb,0,.30a0. Groth in his “ Tabellarische Uebersicht der Mineralien” gives as the most probable formula for romeite CaSb,0, and for schneebergite Ca,Sb,O,, making this last identical with atopite.
A quantitative analysis of the schneebergite had not been made, so it appeared to us desirable to make one with a small amount of clean material. The mineralogical collection here contains a series of specimens of this rare mineral froin Schneeberg, the greater part of which were collected at different times by von Elterlein during his study of the mineral deposits of that locality.
Most of the mineral appears as crystalline aggregates upon the ore, which latter consists of a mixture of magnetite, zincblende and chalcopyrite; the gangue mineral is massive quartz. The aggregates are partly kidney-shaped and consist of rounded crystal grains, with scarcely recognizable form. The color varies from honey-yellow to bright wine-yellow; the surface is often brown from a slight decomposition, the color being due to a thin coating of iron hydroxide. The perfectly fresh, undecomposed crystals are isotropic and occasionally show weak and abnormal double refraction, especially when they contain inclusions of fine particles of the ore.
On other ore-specimens the mineral appears as thin coatings or as a deposit; occasionally can well defined crystals be observed, all of which show the single form of the octahedron. The crystals are generally accompanied by calcite aud breunerite, from which the mineral has evidently originated, as has been shown by v. Elterlein ;t commonly the schneebergite surrounds the calcite, if it has not entirely replaced it. The paragenesis can be followed still better in sections under the microscope. It can be seen that the calcium-iron carbonate changes at first to a light yellow, double refracting mineral of indetinite composition, which by further change becomes granular and isotropic and finally passes into the pure schneebergite.
* Verhandl. d. k. k. geolog. Reichsanstalt, 1880, 313.
+ Jahrbuch der k, k. geolog. Reichsanstalt, 1891, xli, 336; Zeitschr. für Kryst., xxiii, 283.
te added and, altion of any subpacked if the acistill nitric acide of the deconeebergite ared and drieat these were
Some difficulty was experienced in isolating the material for an analysis and extreme care was necessary in order to get a perfectly pure product. The separated particles of ore fell easily by weak pressure with an agate spatula into single isotropic crystalline grains; a microscopical examination of this coarse powder showed an accompanying mixture of magnetite, zincblende, irregular fragments of milk-white quartz, calcite and almost opaque, unknown black particles of a mineral which was unattacked by acids, apparently some silicate; all of these impurities were present only in very small amounts and made at most 5 per cent of the total weight. The material was first digested with dilute hydrochloric acid and afterwards nitric acid was added and, after a short time, warmed in order to be sure of the decomposition of any sulphide present; the granular crystals of schneebergite are not attacked if the acid is sufficiently dilute. The well-washed and dried residue still contained quartz and the black particles, but these were removed mechanically and about 0:4 gr. of the mineral was obtained, which in respect to purity was all that could be desired.
The specific gravity was first carefully determined by means of a pycnometer; the amount of substance used was 0.4110 gr. and the specific gravity found was 3.838 (the average of three weighings from 3.823-3.848). Weidel found with 0.17 gr. the gravities 3.9, 4:1 and 4:3. As the amount of mineral was so small, a qualitative analysis was conducted in a quanti. tative way according to Weidel's results, who, as above stated, found antimony and calcium as the principal elements. The material was fused with potassium and sodium carbonates, with the addition of some nitric acid (in order to prevent the reduction of the antimony); the fused mass was dissolved in hydrochloric acid and there resulted a liquid, colored yellow by the iron present, which contained a substance having the exact appearance of silica. On the addition of hydrogen sulphide a deep brown precipitate was formed, which showed when examined, besides much sulphur from the oxidation of the hydrogen sulphide by the salts of iron, nothing but silica and some platinum, which last evidently came from the fusingcrucible, as fusions containing saltpeter will always attack platinum somewhat. Neither antimony, bismuth nor copper, which Weidel found, were present.
Further analysis of the filtrate gave only iron and calcium and the amounts were Fe,O, 32:33 per cent and CaO 32.58 per cent. An exact determination of the silica could not be made because it was partly used in the qualitative analysis of the precipitate. Professor Groth kindly placed at our disposal more of the material from the museum collection and
about 0.2 gr. of this was prepared. To remove the impurities, the material was treated with stronger hydrochloric acid, which also slightly attacked the schneebergite with the separation of silica. An analysis of the carefully cleaned material gave SiO, 35.45 per cent and Fe,O, 32:11 per cent. The formula for this composition exactly tallies with that of a lime-iron garnet, as the following analyses show :
3Ca0. Fe,0,. 3Si0g. 35.45%
35.43 32:33 32:11
31:50 Ca0 ....... 32:58
33:07 It follows from this examination, with certainty, that the schneebergite in the collection here, of which there is a whole series coming from different sources, is nothing more than a very pure lime-iron garnet, topazolite. The ore specimens came from the same locality as those described by Brezina and analyzed by Weidel. In respect to the color, hardness, microscopic relations, crystal form and the iron and calcium content, our mineral exactly coincides with that described by Brezina, so we make the supposition that the schneebergite is a garnet of the above composition. Our inineral fused in the blast flame to a dark brown liquid, while Brezina gave his as infusible. Our supposition is supported also by the circumstance that Brezina described the material as insoluble in acids; calcium salt of an oxy-acid of antimony would naturally be easily dissolved in strong hydrochloric acid. Apparently, on account of the small amount of very impure material which Weidel had, a mistake was made in the qualitative analysis.
The occurrence is exceedingly interesting, as garnet is seldom found in simple octahedra, and, until the present, a completely non-aluminous topazolite, with the exception of that from the Mussa Alp, has not been observed. The iron precipitate was treated with pure freshly-prepared sodium hydroxide, but no trace of aluminum was found; also the mineral contained no magnesia.
Munich, Bavaria, May, 1895.
ART. XXV.-Native Sulphur in Michigan ; by
W. H. SHERZER.
DURING the past year interesting deposits of sulphur have been discovered in the Upper Helderberg limestone, of Monroe county, Michigan, of which, it is believed, no report has yet been made. Native sulphur has not been recognized as