ITS MICEOSCOPIC CHARACTEES. 167 



1-ounds grains of metallic iron (Plate III. figure 3). The common ferrugi- 

 nous staining and the granular structure of the groundmass is shown to a 

 greater or less extent in all the figures of meteoric peridotites given in the 

 plates. 



The chromite or picotite occurs in dark-brown to black, opaque to trans- 

 lucent o-rains and octahedrons. 



An entirely crystalline form of saxonite occurs in the Manbhoom (India) 

 meteorite, which Tschcrmak has described as composed of a greenish-yellow 

 granular mixture, in which bronzite and olivine have a nearly equal color. 

 Besides these, there are numerous grains of pyrrhotite and little grains of 

 iron. In the thin section granular olivine is seen to be the principal consti- 

 tuent. This is traversed by fissures, and has few inclusions. Bronzite occurs 

 in rounded or elongated grains, with a fibrous structure, and both it and the 

 olivine have a pale-green color. Furthei-, the rock contains colorless grains 

 of plagioclase (?) and roundish opaque pyrrhotite and iron grains.* 



The next variety is formed by the addition of diallage, but otherwise the 

 structure remains the same. The diallage shows not only the common lon- 

 gitudinal cleavage, but it is also much cut by an irregular augitic cleavage, 

 thus enabling its ready separation from enstatite in some cases. It other- 

 Avise is closely like the enstatite in its general characters and in its inclu- 

 sions (Plate III. figures 5, 6). 



Sometimes the Iherzolite variety of the meteoric peridotites is found to be 

 entirely crystalline, and in this case the chondri and base are wanting, and 

 the rock is composed of a crystalline granular aggregate of olivine, enstatite, 

 diallage, iron, pyrrhotite, and chromite. In this the olivine contains irreg- 

 ular masses and globules of iron ; while the enstatite and diallage liave the 

 same inclusions, not only of iron, but also of olivine grains. 



In the next type augite is added, but it makes no essential change in the 

 general characters of the rock. In some of the peridotic meteorites, plagio- 

 clastic and possibly orthoclastic feldspar, peckhamite, schreibersite, graphite, 

 etc., occur in subordinate quantities. 



The microscopic study of meteorites is yet so incomplete that it is pos- 

 sible that other types and characters may be later added. 



In two cases a fragmental or brecciated structure has been seen, giving 

 us tufaceous meteorites, which, otherwise than this, show the connnon clion- 

 dritic characters. 



* Die mikros. Besch. meteoritcn, 1SS3, i. 10; SItz. WIeu. Akad., 18S3, Ixxxviii. (1), 362, 363. 



