252 Transactions of the South African Philosophical Society. 



from 300 to 600 feet towards the boundary dividing Vryburg from 

 Maf eking, and this constitutes the watershed. Beyond this, both to 

 che north and north-west, we find a gently rolling country with a 

 gradual fall towards the Kalahari. 



On the south drainage is effected by the Dry Harts River, while 

 on the north are various tributaries of the Molopo, namely, the 

 Mosita, Setlagoli, and Maretsani Eivers, and the Ramathlabama 

 Spruit. To the west are the Mashowing and Kuruman Rivers. 



In the east there is comparatively little vegetation, most of the 

 timber having been cut down for use in the Kimberley mines or 

 destroyed by bush-fires, but west of the railway, and at a distance 

 of from 20 to 30 miles from it, the country is usually covered with 

 large thorn trees, while the ground is thickly grassed. 



The existence of such an abundant vegetation in a district where 

 surface-water is usually absent invariably impresses the traveller 

 with amazement. 



Geology. — Over almost the entire division of Mafeking, and west- 

 wards through Genesa, the basement rock is granite and gneiss, but 

 exposures are not frequent on account of the considerable depth of 

 reddish-yellow sandy soil produced by their disintegration. To the 

 north and north-east of Vryburg, and again at Mafeking, are exten- 

 sive flats formed by diabases and amygdaloidal rocks, these being 

 later than the granite and having a considerable development in the 

 adjoining portions of the Transvaal. 



At Vryburg is the north-easterly termination of the Campbell 

 Rand limestone and dolomite — a formation that constitutes the 

 immense Kaap Plateau. It stretches westwards as far as Kuruman, 

 and then turns northwards, passing in a broad belt through 

 Morokwen towards the Molopo River and the Bechuanaland 

 Protectorate. 



At Vryburg and further south, in the Dry Harts River valley, 

 there are depressions in the older rocks, that have been filled in 

 with shales and boulder-clay belonging to the Dwyka formation. 



Subsoil water. — Rain falls in the summer-time principally, and 

 commonly in the form of thunder-showers. 



The Dry Harts River runs during a portion of the year, but north 

 of the watershed the rivers only come down after continued thunder- 

 storms. The flow is, however, soon lost in the sand of the river- 

 beds, and in the Molopo, below its junction with the Setlagoli River, 

 running water is seldom found. 



By digging shallow pits in the beds of the rivers the natives obtain 



