GEOLOGY OF CENTRAL MINAS GERAES, BRAZIL 423 



valley slope into the Jequitinhonha River. This has resulted in 

 the following distribution of the diamond-bearing deposits. Nu- 

 merous remnants of chapada deposits still occur upon the plateau in 

 areas as yet undissected by the rejuvenated streams. Gravel 

 deposits of later age occur lower down on valley terraces at various 

 elevations above the present stream beds. Gravel and sand 

 deposits of still more recent age occur along the present stream 



Fig. 25. — Stirring up the mortar-lilce mass of diamond-bearing clay and gravel 



bottoms. All these deposits contain diamonds in greater or less 

 abundance. 



The present-day practice for the recovery of the diamonds is 

 simply a furtherance of the process of concentration which has been 

 going on in nature. When a considerable quantity of soft kaolin 

 and loose gravel from the diamondiferous conglomeratic deposits has 

 been accumulated in the bottom of the trench, or mine, a stream of 

 water is conducted through the trench (Fig. 24). As the running 

 water passes over this loose material, natives armed with a sort of 



