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O. A, Derby— Occurrence of Gold in Brazil. 441 
place consists of hydromica schists with granular quartzites 
(itacolumite) and itabirite. The region abounds in old alluvial 
washings and rock mines in quartz, itabirite and pyrite, those 
in the latter material being the most important. The geolog- 
ical formation at the Sabara bridge is identical with that of the 
country rock of the great pyrite vein at the celebrated mine 
of tail Velho some fifteen miles away. 
become lined with a crust of black botryoidal limonite less 
than a millimeter in thickness. The greater portion of the 
men. This film, though very thin, is of appreciable thickness 
and rests on the polished surface of the black limonite, from 
which it may be detached in minute flakes by a very slight 
pressure with a metal point. On various parts of the specimen, 
but particularly along the whole length of the V-shaped streak, 
are minute detached films of gold, the largest of which cover 
a surface equal to about a square millimeter. These gold 
films adapt themselves perfectly to all the irregularities of the 
