of Minos Geraes, Brazil. 27 



and a small amount of ilmenite, tourmaline and rutile, all of 

 which have the appearance of autigenetic elements. 



In the dump a few blocks of harder rock of various types 

 were found which from their rarity and evident sporadic mode 

 of occurrence may be presumed to represent segregated masses 

 in the midst of the predominant type of earthy ore. One of 

 these is a quartz-garnet rock like that already described from 

 Piquiry but without traces of a bisilicate element and with the 

 quartz mosaic in comparatively large grains that suggest a 

 doubt as to whether this mineral is a secondary or primary ele- 

 ment. Another highly quartzose type has as a bisilicate ele- 

 ment an altered mica and has, as an accessory, yellowish isotropic 

 grains that could not be determined but that give a decided 

 titanium reaction. Still another type is a garnet-amphibole 

 rock with rare grains of secondary (?) quartz and with the gar- 

 net full of delicate rod-like inclusions that appear to be acicular 

 amphibole. With the exception of the mica-bearing rock all, 

 of these types are identical with those found at Piquiry, though 

 no case of the formation of the secondary asbestus was 

 observed. 



At the Agua Limpa locality prospecting operations have 

 revealed an extensive ore body which at the surface is com- 

 posed mainly of secondary oxide but with a sufficient admix- 

 ture of garnet to show that this body is also essentially a mass 

 of garnet-bearing rock. A small pit shows underneath the ore 

 a layer of about 20 centimeters thickness of graphitic earth 

 with patches and streaks of white clay and resting on a mass 

 of yellow clay enclosing graphitic patches. The graphitic earth 

 gives much ilmenite but no other recognizable heavy residue, 

 while the white streaks and patches in it give much quartz 

 with a heavy residue of magnetite and malacolized zircon indi- 

 cating that they probably represent apophyses of the neighbor- 

 ing granite. The yellow clay is massive with small patches of 

 earthy iron and manganese oxides, thus resembling closely, 

 except in color, the clay of the tunnel at Morro da Mina and 

 like that giving a residue of fine quartz with ilmenite partially 

 altered to leucoxene. 



In the bed of a small stream a few meters from this pit is 

 an outcrop of perfectly sound amphibole schist consisting prin- 

 cipally of two types of amphibole (actinolite and cummington- 

 nite ?) in a fine mosaic of quartz and feldspar with sphene and 

 a garnet giving a manganese reaction as tolerably abundant 

 accessories. The heavy residue shows a small amount of 

 ilmenite and amongst the smaller garnets yellowish crystals of 

 ideal perfection of form. This rock has every appearance of a 

 recrystallized sheared eruptive, and if so was probably originally 

 of dioritic or gabbroitic type but containing manganese garnet 



