GEOLOGY OF CENTRAL MINAS GERAES, BRAZIL 417 



clay, or clay slightly intermixed with sand, occur, while elsewhere 

 abundant pebbles are scattered through clay or sand matrices. 

 The nature of the pebbles in different parts of the district varies, but 

 the characteristic and dominant pebbles consist of quartzite, 

 undoubtedly derived from the Caraga formation. Associated 

 with these are pebbles of iron formation, quartz, schist, diorite, 

 amphibohte, and other rocks, the association varying in different 



Fig. 22. — The trench at Cadette's mine, northwest of Sao Joao da Chapada 



locaHties. A characteristic but less abundant pebble in these 

 deposits is the diamond. 



Where exposed at the surface the conglomerate is very hard 

 and indurated, but beneath the surface both matrix and pebbles, 

 especially those of quartzite, are in many places soft and friable. 

 This softening of the quartzite pebbles bears evidence of consider- 

 able age of the conglomerate deposits. 



In many respects these deposits are strikingly similar to certain 

 deposits of gravel, sand, and clay which occur along the Appalachian 

 region in the United States. In Georgia these contain bauxite; 



