:9i3.] REGION ABOUT NATAL, BRAZIL. 443 



Quartz-Biotite Schist. — This was found at kilometer 49.5 near 

 the place where the railroad crosses the Ceara-Mirim River, not far 

 from Taipu. The rock is dark-colored, hard, rather fine-grained, 

 containing quartz and biotite in great abundance. Its general 

 appearance indicates that it may have been derived from some old 

 sedimentary series. A slide shows quartz and biotite to be abundant 

 as cemented grains. The feldspars are cloudy and hard to dis- 

 tinguish. Magnetite is scattered through the rock. There is some 

 hornblende and tourmaline present. 



Biotite-Schists.— In the cuts west of Baixa Verde granites and 

 pegmatites cut through biotite-schists. Fresh specimens of these 

 schists have a shiny, black or purple color. When weathered a 

 little, the schists turn a brownish tint. In one specimen collected at 

 the sixth cut beyond Baixa Verde, the following minerals appear in 

 the slide : biotite in great abundance, quartz rather prominent, a 

 considerable quantity of plagioclase and orthoclase, only scattering 

 amounts of apatite and magnetite, and some garnet. Another speci- 

 men of this biotite-schist, which is partly weathered, shows some 

 sillimanite. 



Granite- Aplite. — A specimen from a dike cutting through the 

 biotite-schists in the fifth cut west of Baixa Verde is a medium- 

 grained, pinkish-white granite-aplite. Quartz grains are distinct. 

 Muscovite and biotite are easily recognized in the hand specimen. 

 With the microscope the following minerals were found : orthoclase 

 and quartz are abundant ; plagioclase and microcline are rather 

 prominent ; there is a quantity of titanite ; both muscovite and bio- 

 tite are present ; some garnets and specks of magnetite are scattered 

 through the rock. 



Granite-Pegmatite. — Occurring as dikes, breaking through the 

 biotite-schists, are granite-pegmatites. Some of them are graphic 

 granites, and in some the quartz is scattered through irregularly. 

 All of them are a light pinkish, decomposing to an almost whitish 

 color, the feldspars changing over to sericite. A slide shows the 

 following minerals: orthoclase, plagioclase, and quartz in abundance; 

 microcline, rather prominent ; biotite in patches ; and tourmaline of 

 a very dark variety. In one pegmatite there occurs a vein of red- 



