BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA 



VOL. 17, PP. 377-450, PLS. 47-54 AUGUST 25, 1906 



OBSERVATIONS IN SOUTH AFEICA 



BY W. M. DAVIS 



(Read before the Society December 28, 1905) 



CONTENTS 



Page 



Introduction 378 



The journey .. 378 



Physiographic divisions of South Africa 380 



Problems here considered 381 



Acknowledgments 381 



The Cape Colony ranges 382 



Location and structure 382 



Analogy of the Cape Colony ranges with the Alleghenies 383 



Drainage problems 385 



The Klein Zwartberg and the Wittebergs 389 



Table Mountain range and its fellows 393 



Planation surfaces in the Karroo 396 



The dissection of graded mountain slopes 399 



The Dwyka formation 400 



General features 400 



Extent and stratigraphic relations 400 



The Dwyka near Mat jesf ontein 401 



The Dwyka ridges near Laingsburg 403 



The glaciated Dwyka floor near Ngotshe, Vryheit 406 



The Dwyka at Vereeniging .• 409 



The glaciated Dwyka floor at Riverton and Kimberley 411 



Glaciated Dwyka floors elsewhere 412 



Summary concerning the Dwyka formation 413 



Topography of South Africa in Dwyka time 414 



Climatic conditions of Dwyka time .• 415 



Change of temperature 415 



Changes of land area and form 416 



Ocean currents 417 



The subtropical belt 418 



General refrigeration 419 



Shifting of the poles 419 



The interior highland : the Veld 420 



The scheme of the geographical cycle 420 



The open Veld, a plain of erosion 421 



XXXIV— Bull. Geol. Soc. Am., Vol. 17, 1905 (377) 



