198 ME. G. W. LAMPLTJGH ON THE [May 1907, 



kopje, isolated and of conical shape, lay close alongside our road on 

 the left (north). This hillock was composed of shale with a capping 

 of thin sandstone, apparently resting upon basalt. I made a hasty 

 ■examination (near the end of a long trek), and the rough sketch in 

 my note-book shows the following section : — 



Top of kopje (slopes clad with Euphorbia). 



Thickness in feet. 



Flaggy greenish sandstone 0|- 



Grreen marly shale 3 



Purple shale 6 + 



on decomposed basalt? with platy structure, much 



hidden by talus. 

 Hard amygdaloidal basalt-debris at foot of kopje. 

 Note: Bedding of the shales nearly flat : looked rather promising for fossils, 

 but none found. 



At the time when I saw this section I was of opinion that the 

 basalts were shelving underneath the high ridges of sandstone that 

 lay immediately to the right of our track, not having yet discovered 

 the faulted character of the junction. Consequently, I did not pay 

 such close attention to the evidence for superposition as I should 

 afterwards have done ; but I distinctly remember that bare surfaces 

 of basalt were exposed in close proximity to the kopje ; and this 

 being on the downthrow side of the great fault, it seems impossible 

 that the sediments can have been brought up by the faulting. The 

 spot certainly deserves further investigation, which I hope that it 

 will receive from the next geologist who may pass that way. 



(5) The Chalcedonic Quartzite, Kalahari Sand, and 

 other Surface-Deposits. 



The Chalcedonic Quartzite. 1 



In many places the basalts of the plateau are overlain by a curious 

 •siliceous rock that has figured largely in all travellers' descriptions 

 of the country; for, although of insignificant thickness, it renders the 

 ground which it occupies exceedingly uncomfortable to traverse. 

 Frequently it occurs only as a chaos of loose blocks thickly strewn 

 -over the flats ; but occasionally it attains a thickness of several 

 feet, and from its resistant nature gives rise to conspicuous table- 

 topped kopjes. 



The rock is a hard sandstone or quartzite, sometimes of a 

 greenish tint, though more often reddish-grey or yellow. It is knit 



1 For locally indurated patches in the superficial deposits of our own 

 country, I have proposed the short terms, ' calcrete ' (when the cement is 

 calcareous), ' silcrete ' (when siliceous), and ' ferricrete ' (when ferruginous) : 

 see Greol. Mag. dec. iv, vol. ix (1902) p. 575 ; and despite the etymological 

 faultiness of the first and second, I think that these terms might be very 

 usefully applied to the indurated surface-beds of Africa. This particular rock 

 I should describe, using the above nomenclature, as a ' silcreted' sand. There 

 are strong objections to the application of the term ' quartzite 'to this material. 



