Si:OIMKXTAKV ROCKS OF RHODESIA. 35I 



oxide. Paler pinkish to brownish beds also occur, and are 

 sometimes markedly false bedded {e.g., Forest Vale). The 

 bedding is generally almost horizontal, and dips of over 5° are 

 very rare, though at Pasipas, twelve miles north of Biilawayo. 

 they are locally much steq^^r. The direction of dip is nearl}- 

 always northerly, showing that the Zambezi occupies a synclinal 

 fold. There are. it may be remarked, no extensions of the beds 

 which occur in the Limpopo basin on to the plateau, and it is 

 also noteworthy that even those of the Zambezi basin onlx 

 stretch on to the plateau in Matabeleland, except at one point 

 in the Charter district, which belongs physiographically to that 

 ])rovince rather than to ]\Iashonaland. In age these rocks are 

 evidently younger than the coal-bearing series which is ex- 

 posed by denudation to the north of the, area we are considering 

 They are. in fact, probably equivalent to ])art of the Stormberg 

 beds of the Cape and Xatal, and to the Bushveld sandstones of 

 the Transvaal, that is to say, they may belong to the Jurassic 

 period, though at one time I was inclined to rank them as 

 possibly of Tertiary age, owing largely to the freshness of the 

 associated volcanic rocks. The thickness of the series is diflfi- 

 cult to estimate, as they are nowhere exposed in their normal 

 relations with beds overlying or succeeding them in true 

 stratigraphical sequence. Tt cannot, however, be many hundreds 

 of feet, apart from the intercalated volcanics, which must often 

 be much thicker than the whole of the associated sediments. 



N'oLCANic Rocks. — The volcanic rocks to which we have 

 referred occur either as isolated flows or sheets among the sand- 

 stones, which is the common mode in our area, or else as vast 

 accumulations of unknown thickness, as in the \^ictoria Falls 

 region. Though basic, they are generally fine-grained and free 

 from olivine, being made up of labradorite laths and grains of 

 augite. Glomeroporphyritic aggregates ( or composite pheno- 

 crysts) of felspar or felspar and augite are characteristic. In 

 most of the occurrences of the plateau there is an extraordinary 

 uniformity in ty]:)e. There is. however, an occurrence of augite 

 andesite near the Insese River. Whether w^e are always dealing 

 with lava-flows is somewhat uncertain. The rocks within a 

 radius of forty miles from Bulawayo are seldom more than 

 slightly vesicular, though further ofif there are cimte scoriaceous 

 types, which are obviously lava ( i.e., near the Gwai-Khami 

 jtmction). Under these rocks, moreover, there may often be 

 seen an induration of the sandstones (e.g., Taba-z-Indima 

 Esipungwene, etc.). This is not more than a few inches, or at 

 most a foot from the junction, though it is sometime? enough 

 to give rise to a prominent ledge on the hill slopes, and in one 

 case (Umfazumiti) has apparently been instrumental in preserv- 

 ing a flat top to the hill after the removal by denudation of the 

 basalt. When iX. is considered that the cement of the sand- 

 stone afl^ected was usually opal, there is removed the principal 

 reason we might otherwise have for regarding tlie alteration 



