;»or. JoUHXAL OF THE DEPARTMENT OF AGRICULTURE. 



and lime cuutent that varies according to the pie.seiiee or absence ot 

 calcareous nodules in the parent rock. If the analyses quoted under 

 ■' Cave sandstone " higher up may be relied on as typical, the soils 

 From the )ed beds should contain more jjotash than the soils from the 

 cave sandstone, a point which appears to be brought out by the 

 chemical analyses of the soils. 



Moltetw Beds. — These beds derive their name troiu the higliei- 

 lying ground of the Molteuo Division. Reference to the map on 

 Plate III shows that they occupy the flats on the farms Paarden- 

 verlies, Kalkfontein, and Kraaifontein, from which latter farm a 

 tongue proceeds up the kloof which passes the homestead of AVitkoj). 

 'i'he fiats of all ot the other farms are occupied by red beds. 



The Molteuo beds consist of alternating grey or yellow shales and 

 gritty sandstones. The lattei' frequently contain much potash-felspar 

 and some mica, but calcareous nodules are never found. The finer- 

 grained sandstones are loose in texture and weather easily. Nothing 

 seems to be on i-ecord regarding the phosphatic contents of this group : 

 a sample from the neighbourhood of Stomiberg Junction was, how- 

 ever, found to contain 0.06 per cent, of phosphoric oxide — a very low 

 figure. In other areas the Molteuo l>eds have a poor leputation as 

 soil producers, a reputation that is nunntained in the sand-bult soils 

 of Paardenverlies ; the type of soil is sandy and of a degree of fineness 

 that varies according as the soil is derived from sandstones or shales. 



Dolcrite Intrusions. — Dolerite is the name given to the heavy, 

 dark, hard igneous rock which occurs in more or less rounded shapes 

 0)1 the boulder-strewn kopjes of the Karroo, or in massive foini 

 capping the hills and mountains. It must not be presumed, howevei , 

 that dolerite is confined to the Karroo, for it is to be found from east 

 to west of the central portion of South Alrica. When freshly biokeji 

 it is bluish black in colour, although the more acid varieties are some- 

 what ])ale]'. Typical d(deiite contains the following minerals: — 



Labradorite (lime-soda felspar). 



Augite. 



Olivine. 



Magnetite. 

 All of the^e minerals, it will be noted, occur in the ^oiciinic l)eds 

 described above. Several analyses of dolerite have been published, 

 and according to Rogers and Du Toit ■ the following may be taken as 

 typical : — 



/'t'r coil. 



Silica -I'J.T 



Alumina 11.4 



Ferric oxide 9.0 



Ferrous oxide vJ.T 



Lime Il.ti 



Magnesia 7.4 



Potash 0.7 



Soda 2.15 ■ 



Water 1.4 



.Vdded to these we have found 0.17 per cent, of })hosi)horic uxide in a 

 sample of doleiite from the Stormberg area. It would a])pear that 

 the phosphoric oxide occurs as needles of apatite. 



'■' "The Geology of the C§pe Colony." 



