Notice of the Descoberta Gold Mine, in Brazil. 
 
 By Wh. JORY HENWOOD, Esq., C.E., F.R.S., F.G.S., 
 
 &e,«cc,Jcc, 
 
 Chief Commissioner of the Gongo Soco and Catta Preta 
 Gold Mines; 
 
 The ancient Gold mine of Descoberta is about seven miles from 
 the small town of Caethe, and sixty miles N.N.W. of the city of 
 Ouro Preto; on the southern side of the high isolated mountain 
 of Piedade. 
 
 (a) The mountain consists of a schistose rock of specular iron- 
 ore and quartz, alternating in very thin laminae, which bear about 
 N. and S. (magnetic), and dip towards the east. Near Descoberta, 
 some of the beds contain oxide of manganese and mica (jacotinga), 
 and afford traces of gold. 
 
 (V) The ferruginous rock is overlaid by clay-slate, which occa¬ 
 sionally contains great quantities of mica, and varies in colour 
 from brick-red to pale buff, the darker varieties being sometimes 
 mottled with white. It is very soft and fissile; and the lamination, 
 although in some places much contorted, is generally regular, 
 bearing 10° to 20° E. of N., and dipping 60° to 70° towards the east. 
 
 (c) The slate contains numerous nodules and vein-like masses 
 of quartz, which are, for the most part, coincident with the lami¬ 
 nation, though sometimes they intersect:—it is seldom, however, 
 that one portion of the same quartzose body runs parallel to the 
 cleavage-planes of the rock, whilst another is transverse to them. 
 Some appear at the surface; others do not “ crop out,” but are 
 discovered at some distance beneath: all, however, within very 
 short limits (both in length and depth), alike and invariably dwin¬ 
 dle and die away. Their dimensions are very irregular: and their 
 numerous intersections afford neither displacements (heaves) nor 
 
Mr. Henwood, on the Descoberta Gold Mine. 295 
 
 any other of the phenomena which are sometimes considered 
 indices of relative antiquity. 
 
 (d) In the paler-coloured slate, the quartz is milk-white; in the 
 darker varieties, it is ferruginous (gossan ): both are auriferous, 
 but the more deeply tinted portions are by far the richest. Gold 
 also occurs in the slate; but so sparingly, that it would not repay 
 the cost of extraction, were not the quartz and slate so mixed, as 
 almost to defy all attempts at separation. 
 
 (c) The gold is of the very best quality; but, being naturally 
 somewhat alloyed with palladium, it has a slightly greenish tinge. 
 
 (/) The mine is the property of a rich and influential landed 
 proprietor (fazendeiro), who works it only when his labourers are 
 not employed in agriculture;—the invariable custom of the Bra¬ 
 zilians : and, notwithstanding it is within twenty miles of several 
 establishments in which the recent improvements in European 
 mining have been introduced, it is worked in the primitive and 
 costly manner which I have already described as prevalent in 
 other parts of this Province.* 
 
 Circumstances forbid my offering a more elaborate communi¬ 
 cation, and I regret that this is not more interesting. I should 
 have reserved it until leisure permitted me to add other important 
 details, but I am not willing to omit any opportunity of testifying 
 that time and distance have not lessened my warm and anxious 
 wishes for the Society’s prosperity. 
 
 \\^ c v c t.