PERLITIC OBSIDIAN FKOM PILAS, MEX£CO. 533 



ISfr. RuTLEY, in rt']>ly to I'rof. Judd's remarkH, stated that, 

 ;ilthoiij?h the specimen resembkd a pitchstono in lustre, lie was 

 inelined to believe this due to partial devitrification, as indicated in 

 the paper. It was, however, difficult at times to say positively 

 whether minute bodies, such ns globulites, lonj^ulites, &e., present 

 in a vitreous rock were developed at the time of solidification or at 

 a subsequent period ; but he was disposed to regard them in this 

 case as secondary products. It was fortunate that Mr. Kunz was 

 present and able to describe the locality from which the specimen 

 was derived. 



2p2 



