86 Washington — Pyroxenite and Homblendite in Brazil. 



It is obvious from these, and from the symbols given with 

 the analyses, that notwithstanding their higher silica, the 

 pyroxenites are decidedly more femic than the hornblendes, 

 the former being all centrally in dofemane, while the latter are 

 intermediate toward the salfemane class. This is quite in 

 accordance with general experience, the few hornblendites 

 known falling either in salfemane or dofemane, while the 

 pyroxenites are either in dofemane or more commonly in per- 

 femane. The amount of normative ores in each is negligible 

 and the ratio of pyroxene to olivine about the same but just on 

 the border between the first and second sections of the order. 

 A and C therefore fall in the subrang IY.1. 3 .1.2, which has 

 been recently named hilose by Daly* ; and B in IV.1. X< 1.2, 

 that is, cookose ; the Brazil rock being a cookose-hilose and the 

 Montana rock a hilose-cookose. 



Mode.— The mode of the Maracas rock was determined by 

 Rosiwal's i method: 



Hypersthene 59*4 



Hornblende 29*6 



Olivine 7*5 



Pleonaste 3*5 



100-0 



The amounts of olivine and pleonaste are negligible, so that 

 the rock is a hornblende hypersthenite, or a hornblende bronzi- 

 tite, according to the nomenclature adopted for the hyper- 

 sthenes, just as is the Montana rock described by Merrill. 

 The type specimen of this latter, preserved in the Petrographic 

 Reference Collection of the United States Geological Survey, 

 very much resembles the Brazil rock. It differs in showing a 

 somewhat mottled texture with areas of slightly different 

 granularity and tone, but the greater part is closely like that 

 here described, both megascopically and microscopically, the 

 less abundant, rounded, darker and finer grained areas being 

 finer grained under the microscope, and showing rather more 

 hornblende. Merrill remarks on the cumbersomeness of this 

 name, but refrains from coining a new one because the speci- 

 men described by him was at the time the only known exam- 

 ple of this combination. As the type is now shown to be 

 widespread, I venture to suggest the name bahiaite for this 

 noncrystalline combination of dominant hypersthene and sub- 

 ordinate hornblende with negligible ores and olivine. The 

 name would be of equal classificatory rank with lherzolite or 

 saxonite. In some respects, the} r correspond to the avegacites 

 *Jour. Geol., xix, 297, 1911. 



