218 DIAMOND AND CARBONADO WASHINGS IN BRAZIL. 



iited to ancient or recent transportation from the first. In all the 

 localities examined (Santa Isabel, Chique-Chique, Andarahy, Len- 

 coes, and Palmeiras) their occurrence is intimately associated with 

 a thick bed of conglomerate, which is near the middle of the sand- 

 stone formation above described. This conglomerate represents a 

 deposit of i^ebbles formed at a remote geologic epoch in the same 

 way that pebbles are formed at the present time, and the same as the 

 incoherent conglomerates not yet turned into hard rock, in which the 

 miners look for diamonds. At many places it is evident that a por- 

 tion of the gravels worked by the miners is simply the conglomerate 

 decomposed in situ without having undergone any recent transporta- 

 tion or rearrangement. 



There is thus repeated in this region the jDhenomenon already 

 observed in the State of Minas Geraes, where there are several impor- 

 tant washings in decomposed conglomerate and where, as in Grao 

 Mogol, diamonds have been found embedded in the hard conglom- 

 erate. 



The recent and unconsolidated gravels naturally contain a mixture 

 of the elementary materials derived from all the rocks observed in the 

 neighborhood, but where they are richest it is evident that the greater 

 part of these materials come from the conglomerate or " pedra cra- 

 vada," as the miners call it, which seldom fails to outcrop in imme- 

 diate contact or in close proximity to the most productive washings. 

 It is thus evident that the great, if not the only repository of dia- 

 monds in the region, is the conglomerate or gravel fossilized and 

 interbedded with the great sandstone series that characterizes the 

 Serra das Lavras. 



The heaviest bed of conglomerate exposes an average thickness of 

 from 6 to 10 meters, but it contains at many places thin beds of fine- 

 grained sandstone. As has been said, its position is near the middle 

 of the great sandstone series, so that, in general terms, there are about 

 250 meters of sandstone above it and as much more below it. There 

 are many waterworn pebbles scattered through the sandstone that 

 overlies the conglomerate, as well as thin intercalated beds of genuine 

 conglomerate, and these features give a conglomeratic character to all 

 of the formation from the middle upward. It is not, however, char- 

 acteristic of the lower sandstone, and, together with other circum- 

 stances, leads to the belief that a geologic division should be made at 

 the base of the conglomerate and that the lower beds belong to an 

 independent and older division than that above. It is also a striking- 

 fact that many of the pebbles and rolled blocks embedded in the con- 

 glomerate are identical with the rocks of the underlying beds. 



The conglomerate offers a greater resistance to atmospheric influ- 

 ence than the beds associated with it, and for this reason it produces 



