BRANNER-AGASSIZ EXPEDITION TO BRAZIL 1 93 



belt the rocks have a much fresher appearance than the}- have 

 further inland. Specimens taken at kilometer 281 and at 

 Francisco Sa station, kilometer 290, are described by Mr. 

 Turner as quartz-monzonites.^ 



At Bias Fortes the rocks are quartz-monzonites again. ^ 

 At kilometer 344 and at kilometer 363 bare peaks of exfoli- 

 ated crystalline rock are visible on the right of the railway 100 

 to 150 meters above the valley. About kilometer 345 there is 

 a marked geological change. The quartz-monzonites disap- 

 pear altogether, the rocks are no longer coarse in texture and 

 fresh in appearance, but are fine-grained gneisses, and pro- 

 foundly decomposed. At kilometer 355 the change is still 

 more marked, for from this point to Theophilo Ottoni the rocks 

 are mostly mica and other schists, much faulted, wrinkled and 

 cut by veins. All these rocks are so decomposed that one sel- 

 dom sees a hard rock face in the many and deep railway cuts. 

 "Within seventy-five meters of the terminal station at Theophilo 

 Ottoni is a nearly perpendicular face ten meters high, cut in 

 faulted and decomposed schists filled with small quartz veins. 

 The city of Theophilo Ottoni is in a very hilly country, and the 

 streets of the town follow narrow valleys between the hills. 

 Here and there deep cuts have been made through the lower 

 slopes of these hills for street grades or to make room for 

 houses. Everywhere these cuts are in rock, decayed in place, 

 and the earth is so soft that a knife can be thrust into it any- 

 where. This earth, however, stands up in perpendicular w^alls 

 like stone or brick walls through all kinds of tropical weather. 



^ "F. 79. Quartz-monzonite. Macroscopically a coarse, dark, granitic rock, 

 composed of large feldspars of an olive-green lint, quartz, and black mica. 



"Microscopically composed of orthoclase in large anhedrons, micropegma- 

 tite, plagioclase, quartz, biotite, and brown amphibole. There are present as 

 accessories apatite, iron-oxide, pyrrhotite, titanite, zircon, and muscovite. The 

 plagioclase gives extinctions on 010 up to 16° and is probably chiefly basic 

 andesine and labradorite. " 



2 Mr. Turner says of them: "F, 83. Quartz monzonite. Microscopically 

 composed of plagioclase > orthoclase and micropegmatite > quartz >■ rhom- 

 bic p3'roxene. There are present as accessories iron oxide and apatite. The 

 plagioclase gives extinctions on trace of 010 up to a maximum of 19°, and is 

 probably chiefly basic andesine or labradorite. The rhombic pyroxene is 

 slightly pleochroic, ab, faint reddish, c, light green." 



