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PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Nov. 21, 



Water 3-500 



Copper 63-341 



Iron 1-200 



Silver 0-003 



Sulphuric acid 4-301 



Sulphur 2-102 



Arsenic 21-341 



Carbonic acid 4-032 



Vanadic acid , . . . 0-412 



Sand 0-100 



100-332 



from which it will be seen that even here in Bolivia, so far distant, 

 the same chemical agencies had been in operation, and we find the 

 metal vanadium playing a geological role, if such a simile be 

 allowable. 



As the respective names of " veta " (vein) and " ramo " (branch) 

 denote, the metalliferous beds situated to the east of the fault 

 had most probably, from their lesser thickness, been regarded as 

 branches or offshoots of the former, — a supposition apparently sup- 

 ported by finding in the Mina Cimbani the actual contact of the 

 former with one of the latter (Eamo de San Prudentio) ; and a large 

 hand-specimen in my possession, taken from this point, and kindly 

 given me by General Brown, the proprietor of this mine, shows, as 

 in fig. 4, the two inclined at an angle 



one to another, strongly cemented to- Pig. 4. — Sketch of the Hand- 

 gether, and presenting the peculiar specimen, showing the Fault. 

 characters of each of these different 

 deposits and the adjacent rocks in 

 which they are situated. This circum- 

 stance is naturally due only to the 

 different inclination of the strata on y eta 

 each side of the line of fault, causing 

 the veta to cross the upper ramos ; it 

 is, however, interesting as showing 

 how intimately the fault has been closed up by the grinding and 

 sliding action which accompanied its formation. 



Attempts had been, at various times, made by the miners of Coro- 

 coro to pursue their workings on these ramos through and on to 

 the other side of the fault, and also to discover the representatives 

 of the vetas on the eastern side of the same ; but researches made 

 without any preconceived idea of the true state of the case were not 

 likely to be successful; and, up to the time I left Corocoro, they 

 had not been attended with other results than pecuniary loss. Time 

 did not permit of my making a correct section across this interesting 

 metalliferous district, and so deciding the question ; but a study of the 

 immediate neighbourhood of the fault, and particularly the discovery 

 to the west (and close up to the line of fault) of the upper beds of 

 fine-grained red sandstones, very different from the coarser beds 



Eamo. 



