Carbonados in the State of Bahia, Brazil. 483 



The composition of the quartzite as shown by the analysis 

 is about what might have been expected. The pink color is 

 evidently due to the small percentage of iron present in a high 

 state of oxidation. 



It has already heen said that the beds are almost everywhere 

 strongly false-bedded. It is a striking fact that the false dips 

 are not variable in direction as we are accustomed to see them 

 in such rocks, but they are remarkably constant. In the north- 

 ern and eastern parts of the diamond district these false dips 

 are almost invariably toward the north. So nearly universal 

 is this rule that I venture to say that, in the region north and 

 east of Morro do Chapeo, fully ninety -nine per cent of the 

 false dips is toward the north. About Lencoes and south of 

 there south dips are much more common. 



Occurrence of the diamonds. — Most of the diamond wash- 

 ings in Bahia are in stream beds, either actual or abandoned. 

 In other words, the diamonds are found chiefly in alluvial 

 deposits. The position of these deposits, however, shows 

 clearly that the diamonds come directly from the Lavras series. 

 In a great many places the diamonds and carbonados are found 

 in alluvial deposits along streams that flow over the Lavras 

 beds only. Such is the case at and south of Morro do Chapeo 

 and at Campinas. In some of the most productive areas the 

 alluvial deposits have been long exhausted, and the miners now 

 obtain the stones directly from the disintegrating Lavras quartz- 

 ites themselves. Between Lencoes and Andarahy the quarfz- 

 ites have been found so productive that the miners have 

 removed the disintegrated rock down to where it is so hard 

 that it cannot be removed with the hoes, mattocks, and almo- 

 cafres used to scrape it away. 



At Ventura the diamonds and carbonados are found in grav- 

 els that rest upon the Caboclo shales, but the valley is very 

 narrow and the Lavras quartzites cap the hills to the north and 

 west, while the stream itself rises in and flows for many kilo- 

 meters over the Lavras beds, so that there seems to be no rea- 

 sonable doubt that they have the same origin at Ventura as 

 they do at Campinas, a few kilometers to the north, where they 

 are taken directly from the disintegrated quartzites. 



Personally I have never seen a diamond or a carbonado in 

 the original quartzite, but it seems to be a matter of common 

 information that they have been so found. Professor Derby 

 tells me that he himself has seen one such specimen. The evi- 

 dence, therefore, all points to the Lavras sedimentary series as 

 the immediate source of the diamonds and carbonados in the 

 state of Bahia. 



The minerals associated with the diamonds and carbonados. 

 — The question naturally arises whether the diamond originated 



