326 SECTIONAL TRANSACTIONS.— C. 



ultra-basic character with accompanying production of large amounts of carbonic 

 acid. This furnished the motive power for forcing a way through the superincumbent 

 rocks and forming necks, sometimes filled only with the debris of those rocks, but in 

 other cases followed by a weUing up of the ultra-basic magma, frequently itself 

 shattered by accompanying explosions. The associated earth movements being 

 sUght and soon reversed, the supply of molten material was small, and the first 

 eruptions were only succeeded by the intrusion of a few stocks of melUite-picrite or 

 its injection into the ' blue-ground ' as smaU dykes. These last contain no diamonds, 

 so it may well be surmised that the genesis of the diamond was the result of the 

 crystallisation of carbonaceous material derived from the limestone, or of carbon due 

 to the reduction of carbonic acid while the magma was stiU heavily charged with 

 gas before the close of the explosive stage. 



Prof. F. E. SuESS. — The Structure of the Scottish Caledonids. 



July 31 to August 2. 



The Section combined with the International Geological Congress in an 

 excursion in the Witwatersrand. 



Wednesday, July 31. 



A study was made of the rock-groups cropping out in the area and 

 their topographical expression, visits being made to the northerly-facing 

 escarpment, to the Water-Tower Hill and to Klipriversberg. 



Thursday, August 1. 



A traverse of the syncline was made in motor-cars by way of Heidelberg 

 to Blinkpoort. Here the glacial origin of certain Pre-cambrian Strata was 

 confirmed by the discovery of a number of striated and facetted pebbles. 



Friday, August 2. 



The members were conveyed in small parties to a number of the Rand 

 gold mines. The attention of some groups was confined to the methods 

 of crushing the ore and extracting the metal, whilst others examined the 

 underground workings. 



Saturday, August 3. 



Joint Discussion (Sections C, D, K) on Gondwanaland. (Prof. D. M. S. 

 Watson, F.R.S., Prof. A. C. Seward, F.R.S., Prof. G. A. F. Molen- 

 GRAAF, Prof. 0. Abel, Dr. A. L. du Toit, etc.) 



Prof. D. M. S. Watson, F.R.S. — A land flora charact€rised by Glossopteris is 

 widespread in South Africa, India, South America, Australia and other land masses 

 in the southern hemisphere, in rocks of late Palaeozoic age. This flora is accompanied 

 by a reptilian fauna of which Dicynodon is the most characteristic form in South 

 Africa and India, and both fauna and flora were unknown in the northern hemisphere 

 until about 1900. It was therefore natural to believe that they had come into 

 existence in a great southern continent, Gondwanaland, completely separated by sea 

 from that which occupied the northern hemisphere. 



Fossil vertebrates provide admirable material for testing the truth, or at least the 

 necessity, of this hypothesis. 



The only known Lower Carboniferous Amphibia occur in rocks of Coal Measure 

 facies in Scotland. The descendants of these animals are found in similar forms in 



