438 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [May 10, 



Eastern Pro\'ince were not separable from the clay-slate. It would 

 follow from this that the horizontal quartzite resting on the edges 

 of the clay-slate, must, if the latter proved to be Devonian, be much 

 more recent ; and, in an article in a local Magazine*, I conjectured 

 that it might turn out to be an outlying mass of the Dicynodon-for- 

 mation. 



All these conjectures, the verification of which would involve a 

 complete change in the Palaeozoic geology of all but a small portion 

 of the Colony, were founded mainly on the belief in the extensive 

 prevalence of the relation mentioned, due, as I thought, to a meta- 

 morphosis of rocks of widely different ages into masses of the same 

 character. 



Acting on this faith, I commenced to search, and I stimulated 

 others to search, for the evidence which has now established the 

 truth of most of my conjectures, and rendered them all so far pro- 

 bable that they may be fairly assumed as true until disproved. I 

 will very briefly lay this evidence before the Society. 



1. In the Map published by this Society ten years agof the 

 "Primitive Clay-slate," separated from the Devonian schists (" Upper 

 Silurian" of the Map), as shown in the section (pi. 21, fig. 1.), extends 

 eastward to near Gamtoos Eiver. To prove the Devonian character 

 of these schists, I have the fossils that were sent to England some 

 years ago from St. Erancis Bay ; also specimens of Orthis and Spirifer 

 from Humansdorp, and some Encrinites from near Kropame River, 

 all pronounced Devonian by Mr. Salter and other competent autho- 

 rities. And Mr. Thomas Bain writes me that he has found Orthis 

 jpalmata, the Spirifers and Strophomenas, and some of the Trilobites 

 of the Bokkeveldt rocks in the schists near the Knysna, about 

 eighteen miles from the granite, where they dip at an angle of 80°. 

 The specimen of Knorria now exhibited was found by Dr. White in 

 the clay-slate of Zwellendam ; and Mr. Fairbridge tells me that a 

 Trilobite, which he believes to be Homalonotus, was found at the 

 Buffeljagts Eiver, near Riversdale. Now Lichtenstein, Bain, Krauss, 

 and Wilie all agree in making the Cape Town slate and that of 

 Zwellendam and the Knysna belong to one formation ; and the gneiss 

 of Namaqualand is considered by them to be a metamorphic condi- 

 tion of the same rock. Having then proved the Devonian character 

 of a large part of this formation, it is clear that we must colour as 

 " Devonian " that portion of the clay-slate which extends as far 

 west as Zwellendam, and that there is no reason to doubt that the 

 rest of the old rocks, including the gneiss, are of the same age. 



2. I believed the " Carboniferous rocks " of preceding geolo- 

 gists to be Devonian, because they have the same relation to the 

 quartzite as some of those just described ; and I had clear evidence 

 that they had undergone the sihceous metamorphosis. The discovery 

 of Devonian fossils in immense numbers (and among them several 

 new genera and species), at "Winterhoek, Uitenhage, Chatty, Olifants- 

 hoek, and Port Francis, has established this beyond a doubt. The 



* Eastern Province Monthly Mag. vol. ii. 1857. 

 t Trans. Geol. Soc. (2nd ser.) vol. vii. pt. 4, pi. 20. 



