266 



PEOF. A.. H. GEEEX ON THE GEOLOGY AXD 



covering. It is composed of white sandstone, some so soft as to 

 crumble under the hammer, some reminding one of English grey- 

 wether, and some almost hard enough to be called quartzite. It 

 contains reed-like stems, but some specimens that I submitted to 

 Professor TTilliamson are so badly preserved that he could not 

 determine them. Professor Hupert Jones tells me that specimens 

 in the British ^luseum are casts of the stems and leaves of aloes. 

 Its isolation makes it impossible to determine the relations of this 

 mass to any of the neighbouring rocks, but it is perfectly possible 

 that it may be only a mass of the sandy superficial deposit bound 

 together by a siliceous cement. 



lY. Stjmmaet. 



It may seem bold in me, my conduct may be thought to deserve 

 even a harsher epithet, if, on the strength of a few months' scamper- 

 ing over the conntry, I take upon myself to construct a geological 

 history of South Africa from the time of the formation of the Table- 

 Mountain Sandstone to the present day. But speculations that had 

 their birth when I was on the ground, and have kept cropping np 

 every now and then since, have gradually blended into a story, 

 which, I trust, hangs fairly well together, and furnishes a tolerably 

 consistent and reasonable explanation of the facts that have come 

 within my knowledge. This I will now give for what it is worth ; 

 if it serve merely as a string on which to thread these facts 

 together, it may have some use as a working-hypothesis. 



The oldest rocks of South Africa come out to day on the north in 

 the Transvaal, where they are largely crystalline in character, and 

 on the south around and on either side of Cape Town, where they 

 are mainly clay-slate with intrusive masses of granite. In both 

 cases the formations that rest upon these old rocks are marked off 

 from them by the strongest possible unconformity. Whether the 

 crystalline rocks of the north and the clay- slates of the south are 

 parts of the same great group, our present knowledge will not 

 enable us to say ; but it is not unlikely that this is the case, and 

 that beneath the sedimentary rocks which I have been describing in 

 this paper, there stretches an unbroken floor of much older rocks 

 very largely crystalline in their character. Not unlikely ; because 

 in such a case the geological structure of South Africa would 

 correspond in this respect with what is now coming to be generally 

 accepted as the geological structure of Europe, America, and, indeed, 

 every country whose geology has been sufficiently gone into. I do 

 not care to push the parallel further, aud, by dubbing these old 

 rocks " Archaean " or any similar name, to force a correlation 

 between them and the fundamental rocks of other countries : it is 

 enough for me that they are very probably there, and I will speak 

 of them as the " Basement Eocks." 



We may look back, then, to a time when South Africa formed 

 part of a continent made up of these " Basement Eocks ; " subsid- 

 ence began on the south, and a tract was lowered beneath water 



