On the Geological Distribution of Gold. 17 



The thickness of this conglomerate amounts to several feet. In 

 the mass of this rock, but not in the fragmentary particles, 

 gold, in flattened spangles of very small size, is disseminated. 

 In some of the fragments is seen silicious oxide of manganese 

 and some other ores of manganese, occasionally with parti- 

 cles of sub-phosphate of alumina (wavellite) . This conglome- 

 rate exists in the mining district of Minus Geraes, where it 

 is distinguished by the name of Tapanhoacanga. 



In the same district has also been found and profitably 

 worked, another exceptional gold-bearing rock, viz. : — 



In clay or chlorite schists is seen a large chasm, in the form 

 of a dyke, filled with iron-ore, of a deep brown, nearly black 

 colour, partly decomposed, occupying a width of 200 feet, 

 with an inclination of 45° N. in E. and W. Through this 

 mass traverse numerous seams in the said direction and angle, 

 their thickness varying from one to four inches, filled with 

 manganese, bi-sulphuret of iron, mostly decomposed, and 

 argillaceous per-oxide of iron — a hard iron-clay. The pyrites 

 and the iron- clay have proved very rich in gold of a diminu- 

 tive angular shape. This ferruginous compound, with its 

 auriferous seam, is termed by the natives Yacatinga. 



In the province of Antioquia, of N. Granada, the following 

 auriferous rock was discovered in the year 1840. The locality 

 was visited by the writer soon after. A sloping hill forms 

 the division between the rivers Samana and Barcino. 

 The object of our attention occupied the lower portion 

 of the ridge, and close to the junction of the said rivers, 

 at an elevation of 1620 feet over the watercourse. 

 Throughout the whole mass gold is disseminated in large 

 and also in very small particles of irregular shape, having 

 rough and sharp outlines, partly fungiform ; but among the 

 pyramidal agglomeration of perfectly spherical fragments of 

 the mass occupying the centre of the same, and in the 

 seams forming angular divisions, which are filled with per- 

 oxide of iron and hardened clay, not even traces of 

 gold have been found. At the upper portion of the con- 

 glomerate and close to the surface, three seams of two 

 to three inches width were seen, filled with quartz, 

 some pyrites and hydrous oxide of iron, also some ferru- 

 ginous hard clay, which proved to be very rich in gold. 

 These seams, which extended for a short distance in length 

 and depth, commenced about three or four feet below the 

 surface, and, after having disappeared at a moderate depth, 

 never re-appeared ; nor were any other seams or veins of the 

 kind encountered in this part of the rock. The gold ex- 



