410 G. p. MERRILL ON METAMORPHISM IN METEORITES 



stitial material is to be regarded as original detritus and what produced 

 in place by attrition. 



Again, in the Parnallee stone are frequent occurrences like that shown 

 in figure 1, plate 6, where a porphyritic chondrule has been crowded 

 against a fragment of a twinned pyroxene, bending it to the point of 

 fracture. Still other illustrations of this nature are afforded by the re- 

 cently described Troup stone, an intermediate chondrite.^^ Thin-sections 

 of this show numerous large and small single individual fragments of 

 olivine and enstatite with torn and ragged borders and no remaining 

 traces of crystal faces, completely surrounded by finely granulated clastic 

 material with interstices filled with maskelynite. 



No other conclusion can be drawn, as it seems to me, than that these 

 particles are clastic, and the only question relates to their origin. Are 

 they due to a local crushing and differential movement among themselves, 

 or are they tuffaceous and altogether foreign to their present position? 

 In any case, since their consolidation the stones have been subjected to a 

 rise in temperature sufficient to fuse the feldspathic material which on 

 cooling congealed as a glass rather than in crystal form. This is illus- 

 trated in the section of the Alfianello stone, an intermediate chondrite 

 (figure 1, plate 5). 



These and like occurrences, it should be noted, are interpreted by 

 Eenard as militating against the possibility of a tuffaceous origin for 

 the stones. He calls attention to the frequent slight amount of displace- 

 ment of the shattered particles and correctly argues that such a condition 

 would be practically impossible and wholly improbable were the materials 

 transported as loose detrital tuffs. He therefore argues that the stones 

 of these groups were once crystalline and owe their present cataclastic 

 structures to the dynamic agencies, as already noted. 



In reply to this, attention need but be called to the fact that the dis- 

 placements in these particular instances are indeed too slight to account 

 for the tuffaceous structure in the "Kugelchen chondrite" shown in fig- 

 ure 1, plate 2. They are secondary and of minor importance and have, 

 in my belief, no bearing on the original nature — crystalline or f rag- 

 mental — of the stone. 



Berwerth,*^ it needs be stated, was opposed to Renard's view. The 

 presence of the "Netzbroncit" binding material he thought a direct con- 

 tradiction to the idea of pressure metamorphism. 



"Such a possibility [he wrote] can only be accepted if one considers the 

 netzbroncit as a product of mechanical attrition, which theory can not be ad- 



33 Proc. U. S. National Museum, vol. 59, 1921, pp. 477, 478. 

 "^ Op. clt., p. 14. 



