356 E. C. HARDER AND R. T. CHAM BERLIN 



Both the quartzite and the schist phases are Hght colored, the 

 quartzite being white, Hght green, or Hght brown according to 

 the stage of oxidation or decomposition of its constituents. The 

 light-brown color is due to the oxidation of ferrous iron present and 

 is prevalent near the surface. The schists are usually white, light 

 green, or light gray in color owing to the principal constituent, 

 white mica. 



Batatal schist. — -After the deposition of a great thickness of the 

 coarse clastic sediment which makes up the Carafa quartzite, 

 there came a change in the character of the material being washed 

 into the sea. The sediments became finer, whether owing to the 

 lowering of the land surface from which the material was derived, 

 or to a further advance of the sea upon the land. Whatever the 

 cause, there occurred a slackening of sedimentation as well as pro- 

 gressive fineness. The result was the laying down of a series of 

 varicolored clays which through metamorphism have resulted in 

 the Batatal formation, a light-gray to dark-red, fine-grained, 

 argillaceous schist, which overlies the Caraga quartzite conformably. 

 This schist is perhaps best represented along the base of the Serra 

 do Caraga, though, on account of its softness, it is seldom exposed 

 in outcrop. Not only inconspicuous in outcrop, it is also a com- 

 paratively thin formation, seldom exceeding 30 meters in thickness. 

 At one point, however, along the base of the Serra do Caraga 

 northwest of the village of Cattas Altas, it suddenly thickens to more 

 than 300 meters of schist, while at the same time the overlying 

 iron formation gradually pinches out. The situation is somewhat 

 peculiar and it is probable that the upper portion of the Caraga 

 quartzite at that point is schistose, and thus is indistinguishable 

 from the Batatal schist. 



On the eastern and southeastern flank of the Serra do Caraf a 

 a sheet of serpentinized eruptive rock is found to rest upon the 

 Batatal schist at a number of points. It is seen at Morro da 

 Mina, and is also conspicuous in Boa Vista, near Cattas Altas, 

 extending several kilometers northward from there till cut off by a 

 fault. This serpentine layer always occurs at the same horizon 

 at the top of the Batatal schist and at the base of the iron formation. 

 It is not an intrusive, but was apparently a sheet of basic lava 



