236 MEMOIRS NATIONAL ACADEMY OF SCIENCES, VOL. XIII. 



so far as my observations go, are void of fluid content. Extremely fine, dust-like ingredients abound in the other- 

 wise bright mineral particles, although true microliths seem to be wanting. 



As to the mineralogical nature of the individual compounds, a large number of them are not related to pure min- 

 erals, but consist of stony fragments compacted together with several minerals, or a more or less regular conglomeration 

 of different minerals. 



Olivine undoubtedly takes the first place among the pure mineral particles. Not alone the outer aspect, the color, 

 and the peculiar luster of the larger grains and crystal fragments, indicate olivine, but this determination is sup- 

 ported also in the decomposability of these fragments by hydrochloric acid, by the brown color produced by heating, 

 and by the variegated play of colors upon the thin section in polarized light. Most of the fine-grained split particles 

 consist of olivine, likewise many of the crystalline particles with regular boundaries and many even of the spherical 

 concretions. But even in the dust-like interstitial matter, which seems to bind together the larger fragments, the 

 olivine particles are noticeable, as is proved by the brown color produced by heating. Most notable is the olivine 

 substance in many globules with feather-like markings, combined with a white, feather-striped substance, in lamellar 

 concretions, as it occurs in the radiated fibrous globules. The small olivine scales come out very distinctly after 

 heating, by their dark brown color. That they consist of an olivine substance is proved by treating with hydrochloric 

 acid, whereby they are decomposed, while most of the interstitial lamellae remain unchanged. 



Feldspathic constituents can not be indicated with certainty, although individual colorless needlets in polarized 

 light, show the peculiar yellow and blue colors so characteristic of feldspar, as they were observed with great distinct- 

 ness in large quantity hi the meteoric stones of l'Aigle (fall of April 26, 1803), which contained numerous stony frag- 

 ments interlarded with feldspar needles. Likewise, the chemical analysis proves that at all events feldspathic par- 

 ticles are present in the composition in a very subordinate manner. 



Tolerably fine powder treated for a considerable time with warm hydrochloric acid dissolves a large part of the 

 stony mass — olivine part — with separation of colloidal silicic acid. In the residue, freed from silica by heating in 

 alkali, may be seen very numerous, often colorless parallel-striped fragments, besides a turbid, powder-like remnant, 

 which mostly comes from disintegrated globules. Likewise the fine, black granules, which occur here and there in 

 groups remain undissolved, while the olivine, meteoric iron, and iron sulphide dissolve. The more or less trans- 

 lucent portions, which remain undissolved, have a double fracture and show beautiful colors in polarized light. If 

 this remnant be treated still further with hydrofluoric acid, it dissolves completely, except the fine black granules 

 which pertain to chrome iron or carbon. Since in the dissolution of the stony mass by means of anhydrous barytes, 

 it gives a chrome content, it is highly probable that the black granules are chrome iron. Indeed, I frequently 

 observed, upon heating the powdered stone, a sporadic glimmering as of carbon particles, but I was uncertain whether 

 this did not come from dust particles which did not originally belong to the stone, but were only foreign bodies, 

 mechanically added. If the experiment be changed, so that sections of the stone just thin enough to be quite trans- 

 parent are first heated in hydrochloric acid, the sections still maintain their cohesion. Placed upon a glass plate and 

 carefully treated with caustic potash in order to remove the free muriatic acid, the preparation presents a porous appear- 

 ance, the olivine, meteoric iron, and iron sulphide having disappeared, while the white metal and most of the globules 

 remain unaltered. If the preparation so obtained be examined in Canada balsam with a cover glass to protect it, it 

 falls to pieces under the slight jar caused by putting on the cover glass, and the mass appears as isolated heaps of the 

 white mineral, in separate flakes and round globules which often appear quite free. Moreover, small, light garnet- 

 red bodies in quite regular 5 to 6 sided forms make their appearance, very sparingly, in the thin section. They 

 resemble garnets, but are found to possess double refraction. Color also suggests nosean, but the optical character 

 does not agree with this mineral. 



Concerning the nature of the mineral particles undissolved by the hydrochloric acid, which probably belong to 

 the augite group, only chemical analysis can give any information. But here also much uncertainty exists on account 

 of the presence' of numerous globules likewise insoluble in hydrochloric acid (disregarding the olivine grains) which 

 are neither identical with the white mineral, nor exactly analogous to a pure mineral. Many of these globules approx- 

 imate, in their physical characteristics, the white mineral, but yet show a peculiar sort of Assuring. Others plainly 

 consist of lamellae of various compound minerals, and still others are slightly transparent and white powdery-grained, 

 and frequently show a concentric structure with darker and brighter zones. Often, also, they have a crust-like, dark 

 envelope or a partly dark or partly bright center. Black dust-like granules, which occur in the above chondri are for 

 the most part concentrically arranged. Yet these chondri are not amorphous, since their refraction in polarized light 

 is distinctly colored. The most notable of these chondri are those which appear with very fine radial markings, fine- 

 grained, slightly transparent, and of whitish color. The radial markings are eccentric and do not correspond in any 

 way with the outer form of the chondri. Several systems of marking frequently occur side by side in the same 

 chondri. In polarized light, despite the slight transparency, the colors appear in fascicles, which is slightly sug- 

 gestive of the well-known phenomenon in connection with many variolites. The lamellar combination of olivine- 

 like strips with a similar fibrous, white substance, has been described above. 



Concerning the origin of this most notable ingredient of meteoric stones, Daubree conjectured that it was formed 

 by solidification during a rotary flight through gases, while Tschermak favors the view that it was produced by the 

 rounding of previously solidified fragments through prolonged agitation as would take place in a volcanic explosion, 

 as described by Gleichenberg and others in the case of similar round globules in trachyte tufas. This latter conjecture 

 explains the peculiarity noted in many chondri that their inner fibrous structure has no connection with the outer 

 spherical form. Even in the case of the chondri with distinctly concentric structure, this manner of origin may be 



