TRAVELS IN BRAZIL. ^81 



negroes, but now only by eighty. On the white 

 quartz-slate, which forms the main part of the 

 whole mountain, there is here a thick layer of 

 ferruginous, or iron mica-slate, which is bare to 

 the height of thirty or forty fathoms, resembling 

 steep steel-grey walls. This rock consists of a 

 fine-grained, smoky grey quartz, and steel-grey, 

 small-grained ironglance, which supplies the place 

 of the common mica. It is generally thin, sel- 

 dom in layers a foot thick, often when the pro- 

 portion of quartz is considerable, almost crum- 

 bling, and coated at the rifts, with yellowish 

 brown iron-ochre ; here and there a large foliated 

 massive ironglance, generally undulating, occurs 

 in it. The iron mica-slate runs in hour 22 of 

 the miner's compass, from north to south, and 

 dips in angles of from 50° to 80° to the east. 

 It may contain from 50 to 70 per cent, of iron, 

 according as it is more or less separated from the 

 quartz. We observe transitions into pure iron- 

 glance, but still more frequently into quartz-slate, 

 which constitutes the chief formation, and to which 

 it is only subordinate as a thick layer. Towards 

 the summits of the mountain, this formation is 

 covered by the iron-stone flotz, which we have al- 

 ready described at Villa Rica, in which large pieces 

 of quartz are embedded. TJie greatest and richest 

 pieces of iron-ore, which cannot be broken in the 

 gold-washing, are carried by the negroes on their 

 heads, out of the mine, and piled up at the foot of 



