194 Annals of the Carnegie Museum. 



Thence northward across the valley the sandstone forms two very 

 low anticlinal ridges which are covered by a thin layer of soil. 



The dam site Pogo da Pedra, twelve kilometers north of Sao Joao, 

 is formed by a sandstone lidge, but three kilometers farther north 

 another dam site is formed by crushed, schistose rock. The material 

 contains secondary quartz and resembles an altered sandstone. A 

 large pegmatite dike forms a prominent ledge nearby. Near Brejo, 

 ten kilometers north-northwest of Sao Joao the sandstone is gravelly, 

 and is succeeded on the slightly higher slopes by very hard con- 

 glomerate composed of rounded gravel, which is mixed with boulders 

 composed of angular and subangular fragments. The coarse sedi- 

 ments seem to be derived from the adjacent granitic material. The 

 succession of materials here is like that on the north side of the valley 

 near Souza. On the south side of the valley, in the three places where 

 crossed, the sandstone seems to rest directly on the gneiss, no coarse 

 basal material being in evidence. 



Westward from Sao Joao the sandstone continues, with slight east 

 dip, for twenty-five kilometers, or to within three kilometers of the 

 head of the drainage basin. At this western limit of the sandstone 

 the surface has quartz-gravel, both rounded and angular fragments, 

 scattered upon it for a few hundred meters; then gneiss appears and 

 continues to Lavras, with the strike swinging from northwest to west 

 and the dip diminishing from nearly vertical southward to about 

 thirty degrees. In some places the gneiss is thinly laminated and is 

 better described as crystalline schist; but in the main it is rather 

 coarsely banded, though crushed, material. At I.avras it strikes 

 S. 80° W., magnetic, or about S. 65° W., true. 



Five kilometers north of Lavras the Rio Salgado cuts a small range, 

 the core of which is composed of rock which partakes both of the 

 character of the usual gneiss and also of the muscovite quartzite of 

 Serra de Santa Catharina. It carries less muscovite, but has some 

 garnet, and lenticular veins of quartz and seems to be a quartzose 

 mica-schist, rather than quartzite. The material dips thirty degrees 

 southward and the ridge seems to be monoclinal, as is shown on 

 Plate VIII, fig. I. 



A feature of structural significance seems to be exhibited here in the 

 character of the stream-channel. The gorge is occupied by a pool, 

 partly filled with sand, and the gradient of the stream is determined 

 by a ledge in the channel a few hundred meters downstream. It 



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