412 G. p. MERRILL ON METAMORPHISM IN METEORITES 



(4) The "Netzbroncit" of Berwerth. 

 II. Evidences of metamorphism by pressure. 



(1) The granulation of the radiate enstatite chondrules and their 



gradual merging into the ground-mass. 



(2) The distortion, and at times almost complete obliteration, of 



chondrules of any kind. 



(3) The crushed condition of many of the crystalline particles, 

 (-i) The more compact condition of the stone, with chondrules 



at times so finely imbedded as to break with the matrix. 



The most obvious of the above characteristics are the absence of well 

 developed chondrules in the crystalline chondrites and the presence of 

 maskelynite. As elsewhere stated, it is questionable if the presence of a 

 chondroidal form of any kind may not be regarded as indicative of the 

 one-time tuffaceous nature of the stone in which it occurs. The writer is 

 at present so inclined to regard it. Indeed, he can not conceive of a 

 chondrule of the radiate enstatite or porphyritic form resulting from 

 direct secretion in a molten magma.*" 



There remains for consideration the metallic constituent of stony 

 meteorites, and this with particular reference to its origin and connec- 

 tion, if any, with the subject under discussion. 



That the metal is secondary in its relation to the silicate constituents 

 has often been insisted on by the present writer*^ and others, and its 

 original source variously suggested as a product of reduction from iron- 

 rich silicates or more probably, in the view of the writer, a ferrous 

 chloride. Its apparent secondary nature is shown in figure 3, plate 6, 

 from the gray chondrite of Parnallee. In this and like cases the metal 

 was apparently precipitated around the fragment, causing it to appear in 

 the section as a collar or ring. The manner in which it penetrates into 

 the interstices of the ground indicates its deposition since the granule 

 occupied its present position. The same feature is common in the Culli- 

 son, Kansas, stone, and as this has sufl:ered little or no metamorphism the 

 assumption is fair that the two agencies, metamorphism and deposition, 

 are quite independent of one another. A still better illustration than 

 that furnished by either of the above is shown in figure 4, plate 6, from 

 the Cumberland Falls breccia. It will be noticed here that the metal 

 occurs in plates so thin as to appear on a polished surface as mere threads, 

 at times scarcely visible, which penetrate the interstices, often bifurcating 



^ "On chondrules and chondritic structures :" Proc. Nat, Acad. Sciences, vol. 6, Au- 

 gust, 1920, pp. 449-472. 



*^ See papers on Cumberland Falls and Estherville meteorites, cited elsewiiere ; also 

 Danbru. Geol. Experimentale, pp. 520-522. 



