Mr. Henwood's Notice of the Morro Velho Mine. S^l 



bonic acid ; and to this circumstance we must ascribe the ef- 

 fect of the blue ray as shown by Mr. Hunt's experiments. 



I should feel obliged if you would insert this in the Philo- 

 sophical Magazine, as it would perhaps attract the attention 

 of those who are engaged in experiments on this subject. 

 I am, Sir, your obedient Servant, 



Ormskirk, August 21, 1844. RoBERT HarkneSS. 



LVII. Descriptive Notice of the Morro Velho Mine, Proviiice 

 of Minus Geraes ; and on the Relations heinaeen the Struc- 

 ture of the Containing Rocks atid the Directions of the Shoots 

 of Gold in the Brazilian Mines. By William Jory Hen- 

 wooD, C.E., F.R.S., F.G.S., Chief Commissioner of the 

 Gongo Soco Gold Mines^. 



'^I^HE gold mine of Morro Velho is about 48 miles north- 

 -"- west of the city of Ouro Preto and 10 miles south of 

 the town of Sahara : it has been worked by English compa- 

 nies for nearly sixteen years, but unsuccessfully until within 

 three years past. 



It is situated on the flank of a mountain of considerable 

 elevation ; to the contour of which the metalliferous mass has 

 an approximate parallelism, a circumstance of frequent occur- 

 rence in the gold formations of Brazil. 



a. The rock mostly consists of a dark lead-coloured clay- 

 slate, and occasionally contains traces of chlorite, whilst there 

 are some layers of a dark brown colour, and others which are 

 quartzose and have a crystalline structure. The general bear- 

 ing of the lamination is from N.E. to S.W., and the dip is 

 usually towards the S.E. from 40° to 70°. One series of joints 

 bears about E. and W., and another N. and S. (magnetic). 



b. The direction, dip, and dimensions of the mass from 

 which the gold is extracted are very irregular, and although 

 it has some characters in common with metalliferous veins 

 {lodes), it has others which more nearly resemble the forma- 

 tions of tin ore at the Saint Ives Consols f? Rosewall Hill J, 

 and Balnoon§. The accompanying ground plan is copied 

 from that used at the mine, and exhibits the peculiarities of 

 this formation more clearly than any description could do. 



The most westerly part of the mine is called the Champion 

 Ground, and consists of an assemblage of small veins; these 

 unite with the little Quebra Panella, which dips N. 70°-80°, 

 and is, on an average, about eighteen feet wide, although in 

 this respect it varies very much in different parts. Eastward 



* Communicated by the Author. \ Ibid. p. 237. 



t Cornwall Geol. Trans., vol. v. p. 21. § Ibid. p. 24, 



