178 O. A. Derby—Gold-bearing Rocks of Brazil. 
Art. XVI.—On the Gold-bearing Rocks of the Province of Minas 
Geraes, Brazil; by ORVILLE A. DERBY. 
THE rock series of Minas Geraes, which have heretofore been 
recognized as auriferous, are the gneisses and mica schists o 
the crystalline group, and the quartzites, unctuous schists, and 
iron ores (itabirites), of the less highly metamorphosed group of 
rocks succeeding the crystalline series. o these may be 
added a second group of quartzites lying unconformably on 
the second metamorphic series. In all these rocks the gold is 
in, or in the immediate vicinity of, veins of quartz, generally 
if not always accompanied by pyrites, cutting the beds or 
accompanying the bedding, or in vein-like lines of a peculiar 
clay or iron ore. Ina recent trip down the Rio das Velhas I 
noticed that long after having passed the region in which rocks 
generally recognized as auriferous were exposed on the river 
as rich in gold as are those within that region. At the same 
time trial washings at the mouths of the rivers Parauna and 
Pardo, tributaries which at a short distance from the main 
river issue from the auriferous series about Diamantina, and 
proved that the sands of these streams are much poorer than 
Sopa to the west of Diamantina. In the west of the province 
a newer conglomerate appears to have furnished the diamonds 
of the Jezuetaby and Abacté washings. 
