File:The Quarterly journal of the Geological Society of London (12711282445).jpg

1854.. RUBIDGE — GOLD IN SOUTH AFRICA. 3
are rare and of extremely limited extent. The only alteration I
have observed in the structure and chemical composition of the strata
adjacent to a dyke is a little increase of hardness, and numerous
vertical fissures, giving the rock an appearance of being cut up into
cubical masses. The dykes cut each other in all directions, so that
we have been unable to refer them to any system or systems as to
age or direction. They form the central masses of the mountain-
ranges, which are crowned with precipitous escarpments of the igneous
rocks ; the sloping sides of the mountains being due to the unequal
wearing of the horizontal strata (see fig. 1). With the exception of
Fig- 1 • — Diagram of the Structure of the Mountains of Stratified
Rock capped with Basalt, ^c. in Southern Africa,
iron, which is abundant in both the igneous and aqueous rocks, and
manganese, we have not yet found in the Colony any metal in this
formation.
On my arrival at Smithfield, I found the formation to be the
" Dicynodon strata" just spoken of, still horizontally disposed, and
with no traces of metamorphic action ; fossils, both animal and vege-
table, being found quite uninjured at 3 or 4 feet distance from even the
larger dykes. The stratified rocks were a hard, greenish-white, com-
pact sandstone (becoming brown on exposure), forming good build-
ing-stone, and in layers 10 or 15 feet thick, alternating with other
layers of nearly the same thickness, of a bluish-brown and much
more perishable sandstone, which is common in the whole extent of
the formation. Where concretions of hard blue limestone are found
in this rock, it is generally fossiliferous ; these concretions or nodules
seeming to be connected in some way with the fossil bones of the
Dicynodon, which are often imbedded in them. I did not see any
fossils in the harder sandstone on this spot, though some very like it
contained vegetable impressions in other places.
The plain, or rather the broad shallow valley, in which the gold
was found was bounded on either side by a low range of hills ; the
small brook escaping to the south by a gorge in hills of 1000 or 1200
feet in height. (See fig. 2, p. 4.)
The first spot I examined was the hole where the gold was first
found in the quartz turned up by a jackal, (A) in the sketch-plan.
There were a number of the usual rounded masses of igneous rock
lying about in apparent confusion, which, on close examination, I
found to result from the disintegration of two dykes which formed a
junction just at the spot selected by the jackal for his domicile, at A