220 DIAMOND AND CARBONADO WASHINGS IN BRAZIL. 



This question is one to be solved by the mining engineer rather 

 than by the geologist, but it seems to the writer that the probabilities 

 of a favorable solution are strong enough to justify serious studies 

 and experiments. 



Outside of the region of the Serra das Lavras, properly speaking, 

 which ends on the east in the escarpment covered by the conglomerate 

 extending from Lencoes in the direction of Santa Isabel, the diamond 

 washings on land become rarer or are altogether wanting. At a few 

 points, however, where the bed of Rio Paraguassu and some other 

 places have been worked by diving, the locations are so far from 

 the Serra that it is difficult to believe that the diamonds have been 

 brought from there. The most important of these points is the falls 

 of Funil near Bebedouro and consequently on the eastern margin 

 of the region of sandstone and limestone above described. This 

 fall is formed by a heavy bed of conglomerate quite like that of the 

 diamond region, but which, it seems, must belong to another geologic 

 horizon superior to that of the Serra. Its cobblestones are princi- 

 pally of granitic rocks and the conglomerate rests directly upon rocks 

 of this kind. It seems probable that the diamonds found at this 

 place come from the local conglomerate or from some of the rocks 

 associated with it, but upon this point nothing could be conclusively 

 determined. 



As the geologic series of this second zone is more recent than that 

 of the Serra and hence presumably formed in part of materials 

 derived from it, there is a strong presumption that it is also here and 

 there diamond-bearing. The " formation " or concentrated washings 

 of these gravels taken from below the falls at Funil are quite different 

 from those of Lavras in the greater abundance of granitic elements, 

 presumably owing to the fact that streams flow in above from 

 granitic and gneissic regions. 



As to the geologic horizon to which the two (or three) series of 

 rocks above indicated should be referred, nothing decisive was 

 observed. Search for fossils that might have thrown light on this 

 question was fruitless. For various reasons that will not be men- 

 tioned here, the writer judges them to be older than the secondary 

 rocks to which are referred the diamond deposits of South Africa 

 and those of the region of Bagagem, in Minas Geraes, and that they 

 will eventually be found to belong to the middle or upper part of the 

 Paleozoic. 



The diamond region of Salobro, in the municipality of Canna- 

 vieiras, is especially interesting, for it differs notably from the 

 other diamond-bearing regions of Brazil on account of its prox- 

 imity to the sea (about 60 kilometers) and on account of the absence 

 of marked topographic relief that is generally associated with the 



