THE TRANSACTIONS 



OF THE 



SOUTH AFRICAN PHILOSOPHICAL SOCIETY. 



SOME SCIENTIFIC RESULTS OF A MISSION TO SOUTH 



AFRICA, 



By Professor Seeley, F.R.S. 



[Lecture delivered September 16th, 1889.] 



Your country of South. Africa has been heaved up from the sea by a 

 great compressing force, coming from the south, in consequence of 

 which all the older rocks come to the surface of the country towards- 

 the southern shores. These older rocks, owing to the intense 

 pressure to which they have been subjected, have become folded, and 

 heated by conversion of the mechanical pressure into heat ; so that the 

 water, which they originally contained, has slowly, during the long 

 past ages, dissolved a very large part, if not the whole, of the substance 

 of the rocks, in consequence of which these rocks have crystallised and 

 acquired a new texture, totally different from that which they 

 originally possessed, when laid down as sediments at the bottom of 

 an ocean. In my survey of the country I have necessarily omitted 

 the most ancient and most altered rocks, which lie upon the extreme 

 south of the Colony, and my object has been to study the region 

 which we know as the Great Karoo, and accordingly my attention was 

 directed in the first place to the range of mountains which lie to the 

 south of them, and which we know as the Great Zwartberg Range. 

 These rocks I traversed, under the guidance of Mr. Thomas Bain, 

 who made the Zwartberg Pass road, and having gone along the 

 northern side of the mountains and observed the strongly-inclined 

 condition of the top and of the strata, I passed along the southern side 

 of the mountains, and came up in the Oudtshoorn district, by 

 Schoeman's Poort, through Meiring's Poort, which carries the Oli- 

 fant's River to the southward, and there I saw the wonderful, 

 structure of this range, and admired the rocks, folded in complex 

 folds, turned up on end, and pointing upward and downward, a^ain 

 and again, due south, in thiee grand schemes of contortion ; so that 

 as the range spreads out, it consists of a comparatively moderate 

 thickness of rock, repeated over and over again, owing to the manner 



