162 Till. SAN EMIGDIO METEORITE. 



completely colorless mineral, which between crossed nicols shows evi- 

 dence of polj -synthetic twinning. These are too small and irregular for 

 accurate determination, but from certain indefinite and obscure charac- 

 ters I have felt inclined to regard them as belonging to a mineral of the 

 pyroxene -roup rather than as a plagioclase feldspar. Their appear- 

 ance resembles very closely that of the twinned magnesian pyroxenes 

 obtained by Messrs. Fonqueand Levy in artificial meteorites, and shown 

 in Fig. 1, Plate IV, of their paper.* 



Tin: Olivines. --These occur in the form of both mouosomatic and 

 poly somatic chondri and as scattered fragments in the groundmass. 

 The chondri show a variety of structural features; common forms are 

 those shown in Tigs. I ami 2 (see explanation of plate), and also in Figs. 

 7, 8, and !>. In certain cases they are made up wholly of crystalline 

 granules of olivine with scarcely a trace of amorphous matter, or again 

 show well developed porphyritic crystals imbedded in a very finely 

 granular or even glassy base, or again show a very finely granular 

 almost dust-like and very obscure structure throughout. The porphy- 

 ritic olivines are perfectly clear and colorless, with but few cavities or 

 inclosures, though sometimes including portions of amorphous base. 

 Forms are abundant resembling the polysomatic chondri figured by 

 Tschermak t from sections of the Mezo-Madaras, the Homestead, and 

 the Seres meteorites. They are not in all cases circular in outline, as seen 

 in the section, but are often irregular and fragmental in appearance, as 

 shown particularly in Figs. 7, 8, and 0. Mouosomatic forms, as shown 

 in the upper right portion of Fig. 1, and just to the right of the large 

 enstatite fragment in Fig. 2, are common. These, as a rule, show a 

 more nearly spherical outline than do the polysomatic forms. Occa- 

 sional mouosomatic grate-like forms are met with in which the cross- 

 bars are curved, as figured by Eeusch J from sections of the Tysnes me- 

 teorite, but they very rarely show the colorless border or rind as in the 

 case mentioned. Such forms, as a rule, extinguish simultaneously in 

 all portions, but occasional forms are met with in which there is an 

 evident tendency toward twin development, as shown by one-half re- 

 maining shaded betweeu crossed nicols wdnle the other is light, or as 

 in Fig. 9, where the entire left of the field, the barred portion, shows 

 like orientation, while the smaller granules to the extreme right are 

 crystallographically independent. In these grate like or barred forms 

 the bars at times extend entirely across the face of the choudrus, or 

 again show short and interrupted tonus, as in Fig. 9 and the chou- 

 drns in the upper right of Fig 1. The olivines of the ground-mass 

 are always in the form of fragments, as shown by the colorless areas 

 in Figs. 1 and 2 and also in Figs. 3, 4, and 5. The last three are, I 

 believe, indisputably fragments. Fig. 3 is evidently a portion of a 



'Reproduction Artificielle de divers types de Meteorites, par MM. F. Fuque and A 

 Michael Levy. Hull. Soc. Min. de France, Vol. iv, 1881, p. 279. 

 tMik. Beachaffeoheil der Meteoriten. 



aea Jahrb. fur min., etc., Bed Hind iv, 1885 (1836), p. 473. 



