File:The Quarterly journal of the Geological Society of London (13889856569).jpg

ITDENBUEG AND DE KAAP, TEA^SyAAL, SOUTH AFEICA.
581
i'. South of the Spitzkop mountain is " Grey's Creek," near the
mouth of which is an old heading, driven 60 feet into the hill.
This shows a seam of quartz from 1 foot to 2 feet thick, between
decomposed chalcedolite above and brown sand (? decomposed dio-
rite) below. These beds dip W. at an angle of 5", and underhe the
shales that form the high ground on the west. The quartz seam
here, interstratified with the beds, varies (where opened) from 1 foot
to 2 feet in thickness, and yields an average of 3 oz. 12 dwt. of
gold to the ton.
j'. Upon the farm called "Spitzkop," north of the mountain of
that name, are numerous cuttings made by the miners, nearly all
in shales and flagstones. Towards the east side, however, the more
sihceous beds come in, and where exposed in some open mines,
they are much decomposed, especially the lower few feet resting
upon the saddle of a decomposed diorite dyke. On the east side
of the farm the so-called "rotten-reef" has been rather exten-
sively worked in two claims, where it rests upon the saddle-back
of a decomposed diorite dyke. The numerous quartz-leaders in
the shales "vary even in a few feet from 3 inches to ^ inch in
width ; they vary slightly also in dip and direction. Their average
width may be taken as 1^ inch : their general dip S. 50° to 55° ;
and general direction E. to "W. The direction of the dyke being
W.N.W., the leaders strike it at an angle of about 20 degrees."
In the shales are very many thin veins of quartz, more or less
vertical, which, in the lower 3 to 5 feet, are broken up and indis-
criminately mixed with the matrix, thus forming a so-called " rotten-
reef." This term is also applied to the several feet of strata exposed
above, although less decomposed.
Pig. 2. — Section of " Rotten-Reef,^^ Sjpitzko.).
Shaft, 25 ft. deep.
a. Tilted shales. h, Diorite Dyke.
c. The " rich layer."
The section, fig. 2, shows a shaft 25 feet deep down to the dyke,
along which a drive has been made 35 feet to the jN'.jN'.AV., following
the downward dip of the " rich layer," here consisting of 3 feet of
" rotten-reef," with from 1 to 2 feet of poorer "wash" between it and
the dyke. The shaft is sunk through contorted and partly decom-