406 G. p. MERRILL ON METAMORl'lliyM IN METKORITES 



bedded. Ensislieim, which forms Weinschenk's "Typus I" of normal 

 stones, as shown by my slides, instead of consisting of a glassy base with 

 skeleton crystals or "mit lichtem glas mid massenhaften Bronzitskeletten 

 in der Gronnd-mass,"-^ is an almost holocrystalline, though very irreg- 

 ularly granular, aggregate, with occasional small interstitial areas of 

 colorless material which inclose, usually, small rounded granules of 

 enstatite or olivine and, as a rule, polarized slightly in light and dark 

 colors, as the stage is revolved. This has all the characteristics and habit 

 of maskelynite, which I believe it to be. Nowhere in this or the other 

 stones mentioned do I find appreciable traces of an original undiffer- 

 entiated glass base, such as might result from the rapid cooling of an 

 igneous magma. 



As for the "glassy" border surrounding the chondrules of the Parnallee 

 and other stones of this group, I need only call attention to the fact that, 

 as the stones are plainly fragmental, the border can not be other than 

 secondary. As a matter of fact, an examination with a high power shows 

 that the border is not a true glass, but rather a semivitreous material, the 

 result of an alteration or imperfect sintering of the finer portion in the 

 ground. That this may have been the result of temperature changes is 

 made sufficiently evident by a comparison of figure 2, plate 4, that of a 

 "glass'' bordered chondrule in the Parnallee stone, and figure 3, from a 

 section from a fragment of the Allegan stone, a spherulitic chondrite, 

 that had been heated in a gas blast furnace to the point of incipient 

 fusion on the outer surface. The "glassy" border is identical in appear- 

 ance in both instances. In short, I consider the "glass" in all these cases 

 to be secondary and due to metamorphism, incidental to a partial fusion 

 of clastic material. 



It may be well to note, as bearing somewhat on this reelevation of 

 temperature and sintering problem, that the Farmington, Mclvinney, 

 and Eenazzo stones, in which are conspicuous traces of "glass," are black 

 chondrites, such as Meunier"^ has contended and as subsequently shown 

 in our own laboratory,^'^ can be produced by heating ordinary chondritic 

 stones in an atmosphere poor, if not wholly lacking, in oxygen.-* 



==5 Sitz. der k. k. Akad. Math.-Phys. Classe. Munchen, 1899, 1 Heft. 



2" Compte Rendu, Paris Acad., vol. 71, 1878, p. 178. 



"~ Proc. Nat. Acad, of Sciences, vol. 4, 1918, p. 178. 



-* I do not agree with Kunz and Weinschenk as to the origin of tfee Farmington stone. 

 They say, in the American .Tournal of Science, volume 43, 1892. page 67 : "All these 

 (minerals) are entirely enveloped in an opaque, evidently glassy, magma. . . . It is 

 undoubtedly not a polygenius conglomerate, but was rapidly formed out of the fluid 

 glassy magma." Not merely does the stone contain abundant fragmentary chondrules, 

 as would be impossible were it a direct process of cooling from a molten magma, but the 

 amount of glass is really very small and might much more readily be accounted for as 

 above. 



