448 R. R. Walls — Diamond Pipes in Brazil. 



diamantiferous for hundreds of miles. Many important placer 

 mines are worked in the beds of these rivers. 



The field evidence therefore — the long fissure in the quartzites 

 and the trail of diamonds from thence to the sea — seems to indicate 

 that this was a pipe of igneous origin and the original home of 

 the diamonds. But the sericitic schist with its concretions and 

 crystals of iron-ores which fills the fissure differs considerably from 

 the Kimberlite of the South African mines. Unfortunately also 

 Brazilian geologists of considerable standing have contended for so 

 long that there were no pipes in Brazil equivalent to the Kimberlite 

 j)ipes of South Africa that to establish the fact of their existence will 

 require much more evidence on the general geology of the district. 



Besides Sopa two other mines on the summit of the Serra do 

 Espinhaco exhibit the phenomena of pipes. One of these lies at 

 Boa Vista, some 20 or 30 miles south-east of Sopa. The writer 

 visited this mine and found it being worked und%r the direction of 

 Mr. Drajoer, an engineer who had had considerable experience in 

 the pipes of South Africa and who recognized this as an igneous 

 pipe, though highly metamorphosed. The as|)ects of these two mines 

 are shown on the accompanying plate, where they are seen as long 

 fissures surrounded by the hard horizontally bedded quartzites. 

 The third mine at Sao Joao de Chapada lies about 15 miles north of 

 Sopa, and though the writer did not visit it he was assured by miners 

 who had worked there that it was exactly similar to the mine at 

 Sopa. These three mines occur in separate and distinct outcrops of 

 sericitic schist, and the intervening country is covered entirely by 

 the quartzites. These quartzites appear to be of considerable 

 thickness in the neighbourhood of Diamantina and to lie directly on 

 the crystalline complex. 



The geology of the diamond region of Bahia farther north on the 

 Serra do Espinhaco is now pretty well known owing to the researches 

 of Derby, Branner, and Crandell. The following strata counting 

 from below upwards have been mapped there : — 



9. Recent formations. 



8. Salitre Series. 



7. Estancia Series. 



6. Lavras Series. 



5. Paraguassu Series. 



4. Jacuipe Flints and Caboclo Shales. 



3. Tombador Series 



2. Jacobina Series. 



1. Crystalline Complex. 



With the exception of the first of these they are all sedimentary 

 deposits. The Lavras series is the one which contains the principal 

 diamond mines, and the inference is, therefore, that the diamonds 

 have been obtained from the disintegration of older rocks. This only 

 leaves us five series of strata with their contemporaneous igneous 

 intrusions. Again the general evidence seems to point to the fact 

 that the drainage has always been as at present from the south or 



