BLACK DIAMOND REGION OF BRAZIL. 327 



it may be of somewhat later age. In any case its presence in the 

 vicinity of the diamond-bearing beds suggests that the diamonds of 

 Bahia may have originated in the same way as those of South Africa, 

 and that the cutting down of these old eruptives furnished the 

 diamonds that are now found in the Lavras sediments. If -this latter 

 theory is correct, the diamonds may yet be found in any of the 

 more resisting portions of the newer rocks — that is, in the Minas 

 series or in the Tombador sandstones and conglomerates. It should 

 be added, however, that no such theory would have occurred to the 

 writer in this case had it not been suggested by the well-known 

 •conditions in Africa. 



Geographic Distribution as Determined bt Geologic Struc- 

 TiTBE. — The only other point of special geologic interest is the effect 

 of structure and denudation upon the distribution of the diamond 

 •and carbonado bearing beds. 



Aside from certain patches of soft beds that are probably 

 tertiary, the highest rocks found in the diamond district of Bahia 

 are the S'alitre limestones. These and the Estancia beds were laid 

 down on top of the Lavras series. After the deposition of the Salitre 

 limestones, the region was folded and faulted and subjected fto 

 denudation. In many places the folds are so closely appressed that 

 the rocks stand on edge; at others the folds are but gentle. Denuda- 

 tion has done what one would expect in such a region : In places the 

 anticlines have been removed right down to the underlying Caboclo 

 shales, thus leaving isolated patches of infolded or infaulted diamond- 

 bearing beds around the main central synclinal area. Where the 

 synclinal folds are large, the limestones are still the surface rocks, 

 while the diamond-bearing beds are deeply buried. 



Governmental Neglect of the Geology. — Of all the remarkable 

 things about this I'emarkable region there is none more impressive 

 to the geologist than the neglect it has suffered at the hands of the 

 Government. Statistics of diamond production are necessarily 

 defective, and especially so when the diamond mining industry is 

 scattered far and wide among small operators and individuals. But 

 when the Government places a heavy duty upon these small and 

 easily concealed stones, the statistics of production must be accepted 

 as but little more than suggestions of the total output. About all one 

 ■can be sure of is that many millions of dollars worth of both diamonds 

 and carbonados have been taken from the Bahia mines. 



These facts are mentioned merely to emphasise another fact of 

 interest to scientific men; and that is that, though diamonds have 

 been mined in this district since 184:4 up to the year 1905, the 

 Covernment had never made any geological study of the region nor 

 even a map of it. The miners have been left to expend their money 

 and their energies in the blindest ways imaginable. In 1905 the Secre- 

 tary of Agriculture of the State of Bahia, at that time Dr. Miguel 

 €almon du Pin e Almeida, had the courage to get Professor 0. A. 

 Derby, formerly State geologist of Sao Paulo, to pay a visit to the 

 diamond district. Mr. Derby spent a week or two there, and handed 



