60 
THE GEOLOGIST. 
ranges of quartzite, often unconformable with them, which quartzite 
is continuous M'ith like quartzite conformable with the Devonian beds. 
Whence I infer that the rocks of a tract of country may he so altered 
hy molecular changes common to all (prohahly in the instance of our 
rocks the infiltration of silica), that beds ofioidely different ages may pre- 
sent the same lithological character, and that when horizontal quartzose 
(or calcareous* or felspathic ?) rocks are continuous with inclined 
rocks of the same kind it is not always safe to infer that beds resting 
conformably on the latter are much iiewer formation than those on lohich 
the sandstones rest iinconformdbly, that the beds «, are very far older 
than <?, d, for instance. 
Fig. 2. 
a b c d 
It is my conviction then (though I admit that my evidence is not 
quite conckisive) that the inclined slaty rocks of this Colony, west 
as well as east, all belong one formation, which geologists at home 
have, on the evidence of fossils, pronounced to be Devonian ; and that 
the quartzite is a rock which has undergone a superficial change, and 
may therefore be called metamorphic. This siliceous metamorphosis 
IS associated with other changes. The clay- slaty beds are often con- 
verted into ochry, micaceous, and chloritic schists. 
There is not in the Eastern Province much evidence of ordinary 
metamorphic action, except in the claystone-porphyry of Bain, which 
I regard as a product of metamorphic action, as I shall more fully 
explain hereafter. At the Matland mines, about twent}?^ miles west 
of Port Elizabeth, are slates like those which at Cliatty contain 
Devonian fossils. Some of these have been converted into chloritic, 
hornblendic, and micaceous schists, without any evidence of the prox- 
imity of eruptive rocks. In the planes of bedding of these schists 
are veins of quartz, and occasionally cnrbouate of lime, not very rich 
in copper-pyrites. I regard the hard blue crystalline limestone of 
the same locality, in which lead and zinc ore occurs, as partially, at 
least, metamorphic. At George and other places intermediate be- 
tween Cape Town and here, granite occurs, but as I have had no 
opportunity of examining it, I shall trace the evidences of metamor- 
phic action from Cape Town northward; 
At Cape Town I found granite-veins varying from one to three 
feet to as many lines diameter running parallel with the strike of the 
clay-slate rocks without displacing them, showing, I think, that they 
had been changed in situ. Other veins crossed the strike. Again, 
* I think I saw calcareous beds of which all I have asserted of the quartzite might 
be predicated. 
