394 W. M. DAVIS OBSERVATIONS IN SOUTH AFRICA 



ridges present a strong contrast to several members of the north-and- 

 south mountains which rise near the Atlantic coast in the Cape Town 

 district, and of which Table Mountain range is a well known outlying 

 example. They all consist, like the east-and-west ridges, of Table Moun- 

 tain sandstone, but most of them seem to be of more or less distinctly 

 synclinal structure, or the lower edges of down-faulted masses, while the 

 lowlands between them are not occupied by younger strata, but are worn 

 down on the unconformably underlying Malmesbury series of steep dip- 

 ping slates and quartzites. The ridges are bold, rugsred and barren, as 

 in plate 49, figure 1. 



Over much of this tract that we crossed on the way into the interior 

 from Cape Town the lowlands are reduced to gently undulating local 

 peneplains, apparently with respect to present sealevel, sometimes inter- 

 rupted by domes of intrusive granite, as north of Paarl. A belt of sands, 

 which lies on a slightly depressed part of the lowlands, constitutes the 

 "flats" by which the Table Mountain range is united to the mainland, 

 thus apparently repeating the relation in which the rock of Gibraltar 

 stands to the mainland of Spain. The exceptional height reached by the 

 Malmesbury beds in Signal hill, Cape Town, is evidently due to a recent 

 removal of a cover of Table Mountain sandstone like that which still caps 

 Lions head a little farther south, both of these being only small instances 

 of what Table Mountain range is on a larger scale. 



The contrast thus presented between mountains of the same formation, 

 Table Mountain sandstone, of anticlinal structure in one district and of 

 synclinal structure in another not far away, is manifestly to be explained 

 not by any difference in the age of the two districts, but simply by the 

 difference in the attitude of the resistant mountain-making sandstone 

 with respect to the controlling baselevel in the present cycle of erosion. 

 In the district of the east-and-west ranges the folds of the heavy sand- 

 stone have a relatively deep-lying position: the synclines there are still 

 below baselevel, while the anticlines rise above baselevel high enough to 

 have been stripped of the overlying weaker Bokkeveld beds, and therefore 

 to stand up in effective relief, yet not so high as to be breached along the 

 axis and thus converted into paired monoclinal ridges, as so often happens 

 in the case of the Medina anticlines in Pennsylvania. In the neighbor- 

 ing southwestern district of the north-and-south ranges the general atti- 

 tude of the Table Mountain sandstones, before erosion swept so much of 

 them away, must have been much higher ; for here the anticlines are com- 

 pletely destroyed (their destruction probably having been accomplished 

 in an earlier cycle of erosion than the one now current), and only the 

 lowest-lying parts of the synclines or down-faulted masses now remain. 



