Vol. 59.] SEDIMENTARY DEPOSITS OF SOUTHERN RHODESIA. 277 



country, with roads that give heavy pulling for ox-waggons. West 

 of this point lies the great Kalahari Desert, extending for several 

 hundred miles across this portion of South Africa — a region which 

 receives and soaks up the waters of the many rivers that run towards 

 it from the high country around. The formation of the desert 

 is entirely sedimentary, and the great salt-pans of Karikari and 

 Ntwetwe, the deposits of calcareous tufa, the brackish water in the 

 water-holes, and the traces of old river-courses, are all evidences of 

 a gradually-drying basin of great extent. 



At Macloutsie the surface of the sedimentary beds lies afc an 

 altitude 1000 feet lower than when last noticed at Pasipas Mountain, 

 and here they become carbonaceous, varying from shales to con- 

 glomerates. They are almost at the same horizon as the commence- 

 ment of the carbonaceous beds to the north. The railway crosses 

 several shallow tongues of shales, as at Sisi close by (where some of 

 the fossil plants described in Appendix III, p. 288, were obtained), 

 and then the boundary keeps to the west, and sweeps round at Dikabi, 

 past the indurated Chopong Hills at Palapye, and turns eastward 

 towards the old Macloutsie police-camp. Near there, the contact 

 between the Archaean and the sedimentary beds is hidden by the 

 extensive lava-flows and tuffs of the Tuli district. At Umsingwane 

 Drift on the Pioneer Road, a small outlier of highly-altered fine 

 sandstone occurs, and on the Bubi River, 60 miles to the east, 

 a narrow strip of the Samkoto Series shows between the gneiss 

 and the lavas. Outliers of sedimentary deposits occur farther 

 east towards the Sabi River, and various isolated patches of coal- 

 bearing strata occur in that direction : these seem to be the remnants 

 of a large area of sedimentaries occupj'ing what is now the Limpopo 

 Valley, most of which has been removed by denudation. As we 

 have already seen (p. 274), small areas of sedimentary deposits occur 

 along the southern fringe of the Tuli Lavas, while long ridges of 

 the peculiar fissured sandstone of the Samkoto Series extend across 

 the Limpopo into the Northern Transvaal. 



Sedimentary deposits of varying lithological features thus border 

 three of the slopes of the plateau of Archaean rocks that forms 

 the backbone of Southern Rhodesia. In the Limpopo Valley, only 

 small areas remain, but on the west, forming the great Kalahari 

 Desert, and on the north as far as the Zambesi River, the derived 

 deposits are of great extent — they even stretch beyond that river 

 and abut against the southern slopes of the Zambesi-Kafue water- 

 shed. 



On the south-west isolated areas of fine sandstones occur along the 

 railway-line, and it may be possible that these are but outliers of 

 the beds of the Great Desert, forming some connection with the 

 strata of the Karoo and Kimberley Series. This has only been 

 gleaned by observations in a railway- journey, when portions of the 

 country were passed during the night ; but there seems reason to 

 believe that Rhodesia is merely the north-eastern shore of the sea of 

 sediments which stretches as far as the Karoo. 



Except in the case of the Tuli district, and the distinct break in 



