546 Professor Schicarz — Earth-movements, S. Africa. 



of fault-troughs which let down slices of the earth's crust into 

 pits where the loose Cretaceous rocks were protected by being entirely 

 surrounded by hard ancient rocks. Although these fault-pits are 

 shown in section as ordinary faults, they partake more of the nature 

 of holes caused by tearing along a zone of shearing. One can 

 illustrate their nature by taking a slah of stiff clay and pushing 

 the two ends of it in different directions over a polished table ; in the 

 zone of shear a number of eye-shaped holes will appear, whose shape 

 the fault-pits of the south-western districts of Cape Colony actually 

 have, and it is in these eye-shaped holes that there now exists what 

 little remains over of the Cretaceous beds. 



Fig. 2. 

 Sketch-map of the floor of the ocean south of South Africa, based on the 

 Admiralty charts. The sculpturing of the sea-floor down to 400 fathoms is 

 shown and also the tailing out of the deep trough (rift-valley ?), A, that separates 

 Africa from the Madagascar ridge, and the commencement of another, B, directed 

 to the east. Dotted portion indicates j)resent land surface ; ruled portion the 

 area of the sea-floor that shows evidence of terrestrial erosion. 



If one glances at tlie sketcli-map. Fig. 2, it will be seen why the 

 faults which let down the Uitenhage Beds are connected with, the 

 Great Rift Valley System in Central Africa. The latter comes south 

 through Lake Nyasa and along the Shire River ; then in a curved 

 line there is a fault which forms the western boundary of a rift- 

 valley, the eastern scarp of wliich is hidden under the sea, or, as 

 I have pi'eviously mentioned, is probably represented by the monocline 

 on the west of iladagasear. This great island is again simply a horst 

 like the Colorado plateaux with fault on east and monocline on west. 

 At all events, tlie fault-line from the Shire River turns to the south- 

 east and on the east there are low-lying tracts of land underlain by 

 Upper Cretaceous rocks, forming Portuguese East Africa and 

 Zululand ; a last little patch is left near the Umzamba River in 

 Eastern Pondoland. From here the fault-line forms the actual 

 boundary of South Africa as far as the mouth of the Bushman's River, 

 south of Grahamstown. The deep trough, A, in the sea-floor tails 

 out here also, and the system of faults which lets down the Uitenhage 



