The percentages in all except the first are calculated from the weight found.

From these figures it will be seen that the minerals which go to make up the rocky portion of the meteorite are essentially olivine and enstatite, with considerable pyrrhotite, as is also shown by the microscopical description.

The stone belongs to the class of meteorites to which G. Rose* has given the name "chondrites." To the unaided eye the chondritic structure is not distinctly marked, a broken surface showing a fine grained and evidently crystalline-granular rock, very compact, of a greenish gray color and thickly studded with small metallic points with a brassy luster. A polished surface shows the stone to be composed of small chondri rarely over 2mm in diameter, thickly and firmly compacted in a fine granular groundmass. Throughout the entire mass, are thickly distributed innumerable small irregular flecks of a steel-gray, brassy and bronze-yellow color, presumably native iron and pyrrhotite.

The striking feature of the stone is its fine and compact texture, which exceeds that of any chondritic meteorite with which we are acquainted, but which is perhaps most closely approached by the stones of Dhurmsala, India, and Cabarrus county, N. C.

Thin sections of the stone show, under the microscope, a confused aggregate of rounded and irregular, often fragmental olivine and enstatite grains and chondri, imbedded in a fine granular groundmass of the same mineral composition.

The chondri occur in both monosomatic and polysomatic forms composed either of olivine or enstatite alone or the two

* Abhandl. der Königl. Akad. d. Wissensch. zu Berlin, 1863, p. 161.

minerals associated. The peculiar grate-like or barred forms so characteristic of olivine chondri are here represented, as are the radiating fan-shaped forms of enstatite.

The large greenish microscopic chondri are, under the microscope, seen to be made up of innumerable enstatite granules so arranged as to form oval or fan-shaped areas of radiating columns enclosing large, quite perfectly outlined crystals of the same mineral. These included forms are nearly colorless or merely gray through enclosures of innumerable dust-like particles, and show sharp and well defined cleavages parallel to either prism, and a parting parallel to the orthopinacoid. Both olivine and enstatite are nearly colorless or gray through enclosures of dust-like particles, and carry but few cavities.

In addition to the minerals above mentioned there were noticed occasional broad, irregular plates of a monoclinic mineral, light gray in color but polarizing brilliantly in red and yellow colors and which gave extinction angles varying from 25° to 31°. Such are presumably augite or a closely allied pyroxene. Nothing that can be certainly identified as a feldspar was observed. Occasional small, nearly colorless, angular forms show faint indications of twin structure, and it is possible may be a plagioclase. In two sections were observed irregular outlined interstitial areas, perfectly colorless and full of gas cavities. These in some cases remained quite dark during a complete revolution of the stage, and in others gave decided polarization in light and dark colors, and in converging light showed

2.

indistinct biaxial interference figures. The position of these areas relative to the other constituents is that of an interstitial glass or a secondary mineral, like a zeolite. As they show neither cleavage nor crystallographic outlines, and moreover are to be found but rarely in the sections at hand, it is impossible to identify them satisfactorily.

The metallic iron occurs in the usual rounded and irregular masses one to two millimeters in diameter and is apparently in about equal proportions with the pyrrhotite: the latter showing a bright brassy luster in strong contrast with the silvery white iron.

The black vein above noted traverses the stone in the form of an irregular fissure (often expanding and contracting abruptly as is shown in figure 2), for a distance of about 60mm, and varies in Natural size. width from a mere line up to 2mm. Near its lower end it bifurcates and encloses a portion of the mass of the meteorite some 15mm long by 2mm wide.* From a fragment

* Since the above was written Messrs. Ward and Howell have sliced the stone through the center and published in Science of June 1, 1888, a figure showing the full extent and width of the veins.

containing a portion of the vein thin sections were prepared, and the remaining vein material, separated as clearly as possible from the enclosing rock, was subjected to chemical analysis, the process being essentially the same as in the analysis of the meteorite proper. Although the vein material is more compact and much darker in color, the analysis shows very little difference from that of the mass, the main apparent difference being the absence of the lime-bearing mineral. The following are the figures obtained by analysis on material that weighed a little less than 0.4 grams:

The same difficulty, with regard to water in the mineral, exists here as in the analysis of the mass.

From the figures it appears that the portion soluble in hydrochloric acid is essentially olivine in composition, while the insoluble is evidently a mixture of the same insoluble constituents as the mass of the meteorite. The filling material of the vein is, to the unaided eye, quite black and without luster; under the microscope it is seen to penetrate very irregularly and by innumerable minute vein-like ramifications into the stony mass on either side and to carry numerous enclosures of a colorless mineral substance and blebs of metallic iron and pyrrhotite. The exact nature of the colorless enclosures cannot be ascertained. On treating an uncovered slide with hydrochloric acid a part of these were dissolved, others were unacted upon. Under the microscope they are full of irregular rifts and fracture lines but show no true cleavages. Some of them are in the form of single individuals, others have the structure of fragments of polysomatic chondri. Nearly all contain included black amorphous material and many show distinctly included specks, giving the silvery white and brassy yellow reflections of the metallic iron and pyrrhotite. In many cases they are not separated from the black vein material by sharp lines but seem to pass into it by gradations. Between crossed nicols many of them act like a gum, others remain always light, recalling the well known crypto-crystalline

structure of chalcedony and still show, here and there, occasional small areas giving the characteristic polarization colors of olivine and enstatite. On examining the walls of the vein, areas were observed where the gray and yellowish enstatites and olivines retained their normal properties at the distance of one or two millimeters, but at contact with the black vein matter were reduced to the colorless non-polarizing condition of the enclosures.

The black matter of the vein when viewed in strong reflected light shows a dull bronze luster, less brilliant than that of the pyrrhotite particles which it encloses. The thinnest

portions of the slide when examined with a power of 175 diameters show a brownish amorphous base through which are scattered abundant irregular dust-like particles and flecks of a perfectly black opaque material, the nature of which it is impossible to ascertain by the microscope alone. The structure of the vein is shown in figure 3 in which the finely dotted portions represent the black amorphous vein matter with bronzy luster, the entirely black area, the blebs of metal and pyrrhotite, and the irregularly rounded, clear or partly clouded area, the colorless silicates.

3.

From the study of these veins as above described, we are inclined to consider the colorless particles as olivine and enstatite residuals which have been deprived of their normal optical properties by the forces active in forming the vein. What the exact character of the black and amorphous material may be, still remains a matter of conjecture. It is unacted upon by acids and when tested Portion of vein highly mag- with a needle point it breaks up readily into earthy fragments which are not at

nified.

Mr. Howell informs us that the stone in his possession shows three of these veins, the largest exposure of any one on a broken surface being about four inches. The width and general · character of all, he states, appears to be uniform throughout, though this can be ascertained definitely only by breaking the stone.*

* In structure these veins seem to only remotely resemble those described by Tschermak (Sitz. der Kais. Akad. der Wiss., lxxxv, 1, p. 204), in the Mocs meteorite and which, it will be remembered, he argued indicated an elevation of temperature since the consolidation of the stone, such as aided by reducing vapors and gases fused the iron and pyrrhotite without affecting the silicates. He describes the brown and black Fullmasse" of the vein as an admixture of the same sub

Owing to the small amount of vein material which was available for chemical analysis and the impossibility of separating it completely from the enclosing rock, the results obtained can be regarded only as suggestive. The main points brought out can be best shown by reproducing here a comparison of the results:

These differences are too slight to be considered of great value until found to be constant by further investigation. It is to be hoped that the ultimate possessor of the stone will regard a knowledge of its true character as of first importance and will not hesitate to sacrifice any necessary amount for the purpose of an exhaustive examination by the most advanced methods. Our most sincere thanks are due Mr. Hensoldt for kindly furnishing us with the information regarding the discovery of the meteorite.

Washington, D. C., April 12th, 1888.

ART. XIII.-Evidence of the Fossil Plants as to the Age of the Potomac Formation;* by LESTER F. WARD.

It is remarkable that the geologic age of the formation upon which the cities of Baltimore, Washington, Fredericksburg and Richmond stand should have remained unknown to the present day. My contribution to this subject relates enstance as the meteorite itself, and an opaque, half glassy black admixture resembling the black vein-like material of the Orvinio stone. The silicates occur in the vein in the form of small sharp splinters, the iron in granules and the pyrrhotite in the form of little leaves and small kernels, often so arranged as to give rise to a fluidal structure. Dr. Hans Reusch has described (N. Jahrb. für Min., iv Beil. Band., 3d heft, 1886, pp. 491-2), veins in the Ställdalen meteorite which present features in part common to those of the Fayette stone. To the unaided eye the filling material is black and opaque and carries metallic particles. Under the microscope it shows a brownish gray, isotropic and sometimes opaque glassy substance densely crowded with rounded transparent fragments. The upper figure in his Plate XIV closely resembles in structure the vein matter of the Fayette stone, but as far as can be judged from his description the included particles seem to have retained their normal optical properties. Reusch regards this black vein material as the result of a partial refusion of the chondrite substance.

* Read before the National Academy of Sciences at Washington, April 20, 1888.