c Proceedings of the SoiifJi African Philosophical Society. 



part of this paper consists of an examination of the various agents 

 by which deformation of rocks is affected, and the circumstances 

 under which they act. The main agents are heat, pressure, and 

 solution, which, either singly or in combination, are capable of 

 twisting and crumpling rocks like the hard quartzite of the Zwarte- 

 bergen. Instances of deformation, however, are quoted in which 

 these agents have not acted on the rocks, and the explanation sug- 

 gested is that the crushing is due to the giving way of the crystal- 

 line constituents of the rocks along twin planes. This, which is 

 certainly the case in some instances of the bending of marble, where 

 the calcite crystals are very easily twined, is probably also the cause 

 with sandstones with mud between the grains, the Kaolin crystals 

 being the weak element, and even it may happen in sandstones and 

 quartzites, quartz being now known to have a gliding plane. It is 

 to this cause that the instability of stone building is due. An experi- 

 ment was carried out with pebbles embedded in lead and crushed in 

 an iron cylinder. The main result was the demonstration that for 

 pebbles in a conglomerate to be deformed, there must be separation 

 of the matrix layers. All the results, however, that were hoped for 

 were not obtained, owing to the pressure administered — namely, 

 seventy-five tons — being insufficient. 



Okdinaey Monthly Meeting. 

 3Iarch 4, 1903. 

 Sir David Gill, K.C.B., President, in the Chair. 



The Minutes of the last meeting were read and confirmed. 



The following nominations were made : Messrs. J. Dodt, Bloem- 

 fontein ; P. Havers, Stellenbosch ; and A. Du Toit, of Cape Town. 



Dr. W. L. Griffiths was elected an ordinary member. 



Mr. A. W. EoGERS read a paper on " The Geographical History of 

 the Gouritz Eiver System." 



The Gouritz Eiver is supphed by the Buffels, Dwyka, Gamka, and 

 Traka Elvers from the Great Karroo, and these are joined by minor 

 streams l^etween the Zwartebergen and Langebergen. 



The Karroo rivers had their origin on the southern slope of the 

 watershed of the Colony, which was formed subsequently to tlie 

 great southern anticUnes. The region between and even beyond 



