173 
Miscellanea. 
Apstract oF A Memoir on THE MetTatcirerovs (Gotp) Deposits 
or Brazit. By Wittiam Jory Henwoop, F.RBS., F.G.S., &c. 
&c. &c.* 
[Edinburgh New Philosophical Journal, January 1851.] 
Tue gold-bearing strata consist of granite talcose and clay slates, 
and a granular rock of quartz and talc, locally called Itacolumite,t 
in which the latter is sometimes replaced by oxide of iron. These 
are followed by the Jacotinga,{ the principal auriferous rock, which 
is for the most part composed of specular iron-ore and oxide of man- 
ganese, but sometimes contains talc, mica, and quartz also. A rock 
very closely resembling that beneath the Jacotinga, but generally 
rather less quartzose, succeeds: and this is overlaid in many places 
by calcareous strata. No organic remains have yet been found in 
any of these formations. The gold is either disseminated through 
the rock, and in the short unconnected strings and masses in and 
forming integral parts of the strata—in much the same manner as 
tin ore occurs at Carclaze, and in the small veins at Balleswidden, 
Beam, St. Agnes, and Drake Walls; or disposed in veins or vein- 
like masses as it is at Candonga, Morro Velho, Gongo Soco, Cocaés, 
and Bananal,—or again, in a rounded, sandy, or gravelly state, 
mixed with other detrital matter, in which case, as in that of our 
stream-tin, the quality is far superior to that of the metal obtained 
from mines. A fourth mode of occurrence owes its origin to the 
workings on the other three, for it consists of the finer and lighter 
particles which escape during the extraction and cleaning of the gold 
obtained from the strata and veins, and which are often carried by 
the rivers several miles before they subside. This is obtained from 
the present beds of rivers; and after heavy floods, it is also collected 
from the grass and brush-wood which clothe their banks ; but it is 
wrought only by the very poorest classes, and seldom yields them 
more than a very few penceaday. A rich sample of gold taken 
from the crop of a duck which fed in one of those streams was exhi- 
bited, and this, though very rare, is not a sole instance of the kind. 
The writer once saw the sand and earth scraped by children from 
* Read before the Royal Geological Society of Cornwall, 27th September» 
1850. 
+ From the mountain Itacolumy, near Ouro Preto, which is composed of it. 
¢ From its resemblance in colour to the plumage of a well-known Bra- 
zilian game-bird so called. 
