50 



THE GEOLOGIST. 



ranges of quartzite, often unconformable with them, which quartzite 

 is continuous with like quartzite conformable with the Devonian beds. 

 Whence I infer that the roclcs of a tract of country may he so altered 

 hy molecular changes common to all (prohahly in the instance of our 

 roclcs the inMtration of silica), that heels of widely 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 heds resting 

 conformahly on the latter are much 7i ewer formation than those on lohich 

 the sandstones rest unconformahly , that the beds a, h, are very far older 

 than c, d, for instance. 



Fig. 2. 



It is my conviction then (though I admit that my evidence is not 

 quite conclusive) 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 

 m-otamorphic 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 twenty miles west 

 of Port Elizabeth, are slates like those which at Chatty contain 

 Devonian fossils. Some of these have been converted into chloritic, 

 hornblendic, and micaceous schists, without any evidence of tlie prox- 

 imity of eruptive rocks. In the planes of bedding of these schists 

 are veins of quartz, and occasionally carbonate 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 Ca])e Town northward. 



At Cape Town I found granite-veins varying from one to three 

 feet to as many linos diameter running parallel with the strike of the 

 clay-slate rocks without displacing them, showing, I think, that they 

 liad been changed in situ. Other veins crossed the strike. Again, 



* T iliinlc I saw cakarcous beds of which all I have assorted of tlic quartzite might 

 be predicated. 



