290 



TRAVELS IN BRAZIL. 



foliated, distinct concretions, which seldom allow a fresh 

 fracture, which is uneven, and almost imperceptibly flat- 

 conchoidal. The colour on them is a mean between the 

 brown and blue lead-ore, but shows a yellow tinge passing 

 into siskin-green. 



Some specimens have cellular and small drused cavities, 

 which are filled either with massive or crystallised red lead- 

 ore, of which also massive pieces are found mingled among 

 them. According to the investigation of two chemists it 

 appears that this green lead-ore, exposed with borax to the 

 blow-pipe upon charcoal, gave a sea-green glass ; with alkali, 

 a deep yellow salt ; and with silver, a crimson deposit. 

 Treated with ammoniac there was a blue solution, from 

 which metallic copper was immediately precipitated on a 

 steel watch-spring. Hence, it appears that this fossil con- 

 sists of oxyde of lead, and of copper, and of chromic acid, 

 and consequently belongs to that which occurs, together 

 with the red lead-ore, at Beresof, in Siberia, which was fir^t 

 determined by Mr. Hausmann, analysed by Berzelius, and 

 which is now called vauquelinite. 



The rock, in which the granular quartz, which contains 

 the crystals of the chromate of lead, forms veins, is a clay- 

 slate which owes its origin to mica.' The predominant 

 colour of it, in the pieces now before us, is bluish and yel- 

 lowish grey, which, however, next to the quartz veins, be- 

 comes light grey, nay, almost pure white. It consists of 

 small scales of mica, more or less adhering to each other, 

 which are soft to the touch, and very friable (resembling the 

 earthy talc). Oxyde of iron and chromium give it, par- 

 ticularly near the veins, a brownish cream and orange yel- 

 low. In some places the pearly mica appears in great lustre 

 while the rest of the mass shines only faintly. Compact 

 and loose brown iron-stone, probably originating in pyrites, 

 accompanies the red crystals. As well in the roof as in the 

 base of the quartz veins, the mica scales assume the cha- 



