LYDENBFKG AlfD DE KAAP, TRANSVAAL, SOUTH AiTRTCA. 



571 



the loNTer ground of the head of 

 the valley, it rises into hills and 

 ridges, some of which have a con- 

 siderable elevation. In some cases 

 it has weathered into bare round- 

 ed bosses bearing a striking re- 

 semblance to rocJies moutonnees ; 

 but over the greater part of the 

 area the surface of the granite is 

 decomposed into a soft brown 

 substance very much like an allu- 

 vial loam. 



In the Kaap Yalley the surface 

 of the granite forms an ellipse 

 about 17 miles in length by 10 

 miles in width, with a narrower 

 prolongation in a northerly direc- 

 tion. It widens out again towards 

 the Krokodil E,iver, beyond which 

 it passes in under a series of rocks 

 which rest unconformably upon 

 those with which it has thus far 

 been in contact, and which will 

 probably be found to occupy the 

 remainder of the Kaap Yalley. 



This mass of granite represents 

 a great centre of plutonic up- 

 heaval, of course posterior to the 

 period of the Kaap -valley rocks, 

 which it has greatly tilted all 

 around its margin ; it was, how- 

 ever, anterior to the deposition of 

 the rocks of the overlying uncon- 

 formable formation, as they are 

 still nearly horizontal. 



3. Silurian'? Rocks. — jN'early all 

 around the granite centre is a 

 series of rocks which have been 

 tilted by it into a more or less 

 vertical position. These rocks are 

 siliceous and argillaceous, rarely, 

 and then but slightly, calca- 

 reous, being mainly schists, shales, 

 cherts, and quartzites. I believe 

 them to be " Silurian " rocks ; 

 but, with the exception of an 

 unreliable report of Graptolites 

 having been observed, there has 

 been hitherto (so far as I am aware) 

 a total absence of fossil evidence. 



