866 



0^^ THE METAMOEPHOSIS OE EOCKS IN THE CAPE 

 TOWN DISTEICT, SOUTH AEEICA. 



By De. E. N. Eubtdge. 



I gave, in a paper in the Eebruary number of the ' G-eologist,' a 

 general view of the facts in the geology of this country which have 

 led me to believe that the metamorphosis of rocks is due to a slow 

 and gradual change in their constituents ; of which change water is 

 one of the chief agents, and the internal heat of the earth not a ne- 

 cessary adjunct. 



I now propose to describe more particularly those relations of the 

 quartzite with the palaeozoic rocks, a careful examination of which 

 has rendered necessary an entire reconstruction of the geological map 

 of the country. That map, published in the Transactions of the Geo- 

 logical Society, was the work of an able man, and the evidence on 

 which the Devonian (Upper Silurian, Bain) was separated from the 

 Clay-slate formation was (so far as I have been able to verify it), I 

 believe, such, that he would not have been justified in coming to an- 

 other conclusion by any generally admitted principle of the science ; 

 for this reason, I invite the criticism of European geologists on my 

 facts and inferences, and their aid in solving many difficulties which 

 still remain unexplained. 



I stated in my former Paper that the plains and lower hills and 

 valleys of the coast region, extending from Cape Town to the mouth 

 of the Eish Eiver, were formed of blue slaty and sandy rocks. These 

 were all referred to one formation by Lichtenstein. 



Dr. Krauss, an eminent botanist and geologist, states that he made 

 repeated sections of the country, from the coast to the Karoo, and 

 always found the clay-slate (Thonschiefer und Grauwackeschiefer) 

 occupying the plains and valleys, and the quartzose sandstone or 

 quartzite (Bunter-Sandstein) the mountains. On Zwartkops heights 

 and the Von Stadens river bergen, he remarks this was notably the 

 case. Dr. Atherstone, in a section through the district of George, 

 could find no reason for separating the clay-slate from the Devonian. 

 Mr. Bain agrees with these authorities as to the identity of the slates 

 as far eastward as the mesozoic estuary of the Gamtoos river. In 

 his nuip he shows the clay-slate, interrupted (as also mentioned by 

 Kr:iuss) by masses of granite, and surmounted by sandstones, ex- 

 tendijig from Cape Town to the edge of the mesozoic rocks, — a point 

 corresponding to the Kabeljouw river's mouth in the sketch. 



Lichtenstein, Bain, and Krauss therefore concur in believing the 

 chiy-slate and quartzite of the region between the Kromme and Ka- 

 beljouw rivers to be respectively identical and continuous with those 

 of Cape Town, wliere the highly inclined beds of slate are surmounted 

 by nearly liorizontal sandstone. Mv. Bain, difl:ering with the others, 

 makes both cease here. I have little doubt of tlie continuity of tlie 

 slate from Cape Town hither. I have none (as I shall presently 



