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points in the plateau of Matto Grosso, Occurring either in these rocks 

 or derived from them are gold, copper, platinum, tungsten, mica, marble, 

 talc, apatite, graphite, potash-bearing rocks, precious stones, and build- 

 ing stones. 



Distinctly younger than the Brazilian complex or Archean is a 

 sequence of metamorphic rocks of unquestionable sedimentary origin, 

 consisting of quartzites, schists, limestone, and the great iron-bearing 

 formations of Minas Geraes. These strata occur imbedded in the 

 Archean, which unconformably underlies them and by which they are in 

 part covered in consequence of overthrusting. Their age is indeter- 

 minate, as no traces of fossils have been found, but they are assigned by 

 Branner to the early Paleozoic. 



It is evident that a period of profound diastrophism intervened 

 between the deposition of these "early Paleozoic sediments" and the 

 next succeeding strata, which are sandstones of Silurian (Niagara) age. 

 To the systematic geologist it is a question of some importance whether 

 the deformation occurred in the early Paleozoic or possibly in pre- 

 Paleozoic time, as might be the case if the metamorphosed sediments 

 belonged to the pre-Cambrian. It would seem that we have here a 

 problem not unlike that of the later pre-Cambrian formations of the 

 Lake Superior region which, by some geologists, are considered to include 

 Cambrian rocks. 



These ancient metamorphosed strata are economically of very great 

 importance. They include the enormous iron deposits and the important 

 occurrences of manganese. Gold-bearing veins occur in them, and the 

 diamonds and other precious stones of Brazil are supposed to have been 

 derived from them. 



The Silurian sandstones already referred to are the oldest fossiliferous 

 rocks known in Brazil. They are of Niagaran age and occur on the 

 northern side of the Amazonian geosyncline, dipping gently southward. 

 Branner expresses the opinion that it is highly probable that there are 

 rocks of Silurian age in other parts of Brazil, but none have as yet been 

 identified by fossils. 



Strata of Devonian age occur at widely separated points in Brazil. 

 They are found north of the Amazon, in Sao Paulo and Parana in the 

 south, and in Matto Grosso in the west. They consist of white and 

 yellowish sandstone and black and reddish shales. In the Amazon 

 region, although they dip at a very low angle and are not otherwise 

 disturbed, they are cut by dikes of diabase. In Parana and southern 

 Sao Paulo the Devonian rocks seem to rest directly on the Brazilian 



