Mineralogy of South America. 141 



mineral, still remained. The solution was now acidified with 

 hydrochloric acid and treated with sulphide of ammonium in 

 excess, &c, as in the previous analysis. 

 The results were as follows : — 



Binoxideoftin 18-47 91-80 



Oxide of iron and manganese . 0'53 2*69 



Insoluble matter 1*11 5 '51 



20-11 10000 



Cassiterite from Oruro. — The deposits of tin-ores at Oruro are 

 probably the largest in South America. The ore there occurs 

 both as stream-tin (and is the object of extensive explorations), 

 and also in veins in the Silurian rocks of that district. 



A specimen sent me from that locality was an aggregate 

 of small crystals (pyramidal), of a dirty honey-yellow colour. 

 Blowpipe reactions and chemical examination showed the crystals 

 to be nearly pure binoxide of tin. A determination of their spe- 

 cific gravity at 60° Fahr. gave 6*704. 



Not having visited this district, it is impossible to state whether 

 the Cassiterites are commonly so pure in this locality as the above 

 specimen. 



Cassiterite, Carabuco, Bolivia. — Tin- ores occur extensively in 

 the province of Laricaja in Northern Bolivia, on the west slope 

 of the High Andes range close to the eastern shore of the Lake 

 of Titicaca at Carabuco. They occur here associated with seve- 

 ral minerals containing silver, and in the time of the Spaniards 

 were worked exclusively for the nobler metal : of late years, 

 however, the deads of these mines have been and still are worked 

 for tin. The gossan of these veins, or, as called in the Aymara 

 Indian language, " paco" *, chiefly composed of sesquioxide of 

 iron, is frequently very rich in silver (it is stated, occasionally up 

 to 8 per cent.), probably in the state of chlorides. 



The tin ore is in greatest part Cassiterite, which occurs crys- 

 tallized in prisms, having a specific gravity of 6*4. Mr. Philip 

 Kroeber has forwarded me the subjoined results of his analysis 

 of these crystals. 



Water 1-737 



Tin 76-805\ 



Oxygen 19-534 J 



Iron ....... 2-177 



Silver 0-015 



Tungstic acid .... 0*020 

 Lead 0250 



100-538 



* Which means brown. 



