348 E. C. HARDER AND R. T. CHAMBERLIN 



northern and eastern parts is a series of more or less parallel thrust 

 faults, resulting in several parallel and branching belts of sedi- 

 ments. In the center, occupying the angle between the two syn- 

 clines, is a large circular area of granite, gneiss, and schist of the 

 basement complex raised by this combination of forces into a 

 dome structure. 



A very conspicuous result of the deformation has been the 

 development of V-shaped branchings of the formations in various 

 parts of the area, such as those south of Capanema, west of Cocaes, 

 southwest of Bello Horizonte, and northwest of Serro. These 

 V-shaped junctions can be explained by forces working in different 

 directions at the same or at different times, in such manner that, 

 when breaks occur in the formation, one portion of it is forced 

 against another portion at an angle. Frequently at such junctions 

 there has been much crushing and dislocation of the formations. 



In general the irregularity of deposition, resulting in a great 

 variation of thickness as well as of materials, combined with the 

 complex structural relations above mentioned, has resulted in a 

 condition of complexity of structure and areal distribution of forma- 

 tions not easy to solve. 



PROBABLE ARCHEAN 



Basement complex. — The rocks of the basement complex consist 

 chiefly of granite of varying composition and texture, gneiss 

 with interlayered amphibolite, and micaceous and quartzose 

 schists. Granite and gneiss are probably the most abundant of 

 the rocks in the Archean areas, and of these two the granite is the 

 more commonly observed because of its greater hardness. It 

 forms prominent ridges in many parts of central Minas, and is 

 commonly exposed in rounded bluffs along streams where these 

 flow through granite areas. Crystalline schists are also abundant 

 but are less conspicuous because, on account of the softness of these 

 rocks, exposures are not so common. These schists resemble 

 closely the schist beds in the Piracicaba formation and sometimes 

 can be distinguished from them only by their general distribution. 

 Elsewhere they may be distinguished by their more prominent 

 recrystallization, or by the presence of pegmatite veins. Such 



