112 Transactions of the South African Philosophical Society. 



of which ran in a N.E. direction, parallel to the old southern land 

 surface, and it was here that the greatest depth of sedimentation 

 •occurred. The crust sank under the extra weight in doing so, the 

 underlying beds became strained, and eventually lines of weakness 

 were produced w^hich allowed the molten material beneath the solid 

 crust to force its way upwards in the form of dykes and sheets of 

 dolerite. The sediments thereby became intensely heated, expanded, 

 and tended to decrease their curvature, hence the whole mass rose, 

 sediments and injected dolerite together. The line of greatest 

 ■deposition, and consequent most intense heating, had the greatest 

 relative elevation, hence on emerging from the water the flat lands 

 of the Karroo already had a very well-marked w^ater-parting to begin 

 with, and this is the watershed that still dominates the river system 

 to-day. Where the dolerite had not been injected the strata 

 remained stationary, and on the hinge of the movement a further 

 weakness w^as produced, and that hinge w^ould be situated in the 

 position wliere w^e now find the volcanoes. There are dykes of 

 dolerite in the Stormberg Beds, but there is very good reason 

 to believe that they are of a later date than the central Karroo 

 ones. Given a line of weakness in the earth's crust, there needs 

 no explanation to understand how volcanoes become formed along it. 

 Such are some of the points raised by the discovery of these new 

 volcanoes, and though much may have to be altered later, when the 

 survey of the Colony progresses and new material accumulates and 

 the survey of Natal and Eastern Transvaal is brought into line with 

 our work, yet I have thought it well to bring the points before the 

 Society at this early date because they form an entirely new 

 departure in the way of regarding the structure of our continent 

 and have an important bearing on some of the theories of the origin 

 of continental areas in general. 



places his southern shore Une, along the flanks of the Zwarteberg range, the sedi- 

 ments show no signs of being shore-deposits, and to the south of the mountain-belt, 

 near Worcester, there are occurrences of Dwyka Conglomerate and Ecca Beds that 

 must have once been continuous with those on the north of the mountains, and 

 these also are deep water- deposits. The inland sea that I am referring to must 

 have had its shore line to the south of our present coast. 



