STRATIGRAPHIC GEOLOGY 203 



It has not been my purpose, however, to settle controverted questions 

 in Brazilian geology further than the facts warrant or further than was 

 necessary in order to put the geology on the map in one way or another. 

 I have frankly stated doubts wherever they exist, and I ask the indul- 

 gence of those who may reach different conclusions in regard to the many 

 disputed problems. It is hoped that even the statement of doubts and 

 differences of opinion may help toward their settlement by leading to the 

 accumulation of evidence in the field. The field geologist must therefore 

 feel at liberty to look on the solutions here suggested as working hy- 

 potheses, to be confirmed if found correct, or to be rejected if found 

 wrong. 



In regard to the areas left blank on the map, there is no information 

 available at present. 



ARC HE AN 



General discussion. — The rocks referred to the Archean in Brazil are 

 granites, gneisses, quartzites, marbles, and crystalline schists. Too little 

 is known of these old rocks at present to warrant such a separation of 

 them as has been made of similar rocks in North America ; for that reason 

 they are called the Brazilian complex. Many years ago it was believed 

 that Eozoon canadense, a supposed fossil foraminifer supposed to be char- 

 acteristic of the Laurentian, had been found in the Brazilian Archean 

 near the falls of Paulo Affonso, in the State of Alagoas. Derby said of 

 it : '^Esta descoberta confirma a opiniao emittida pelo fallecido Professor 

 Hartt sobre a idade geologica dos gneiss brazileiro." ^ The supposed 

 fossil, however, is not now regarded as a fossil at all, and no further at- 

 tempt to subdivide the Archean of Brazil has been made or can be made 

 as 3^et. Eocks of the Brazilian complex are found in all of the states, 

 and the area in which they are the surface rocks in Brazil is large, and 

 much of it not yet outlined, while the structure and character of the 

 rocks vary greatly. About Eio de Janeiro and through the Serra do Mar 

 generally they are mostly massive granites and gneisses. In northern 

 Brazil they are more closely folded; ever}- where they are faulted and cut 

 by pegmatite and other dike rocks and traversed by veins of quartz. 



But little is known of the structure of the Brazilian complex. Much 

 information on the subject is scattered through the literature, but widely 

 separated areas can not be confidently tied together with the data now 

 available. Even the "chief lines of elevation or folding'^ suggested by 



2 0. A. Derby: Reconhecimento geologico do Valle do Sao Francisco, p. 11. Rio de 

 Janeiro, 1881, 



