268 MR. A. J. C. M0LYNE5TX ON THE [May I903, 



abundant evidence, in the form of horizontal sheets of vesicular lava, 

 in the volcanic neck, known as Umfazi 'Miti, and in the noticeable 

 induration of the rocks, to show that here was the centre of the 

 volcanic disturbance which has had such a hardening effect on the 

 beds of Thaba 'Sinduna. These flat basalt-sheets continue as far as 

 Shiloh, where they are about 100 feet thick, and break off in sloping 

 hillsides. They lie upon fine red sandstone, which forms the bed of 

 the Umgusa Valley, and across that flat to the west similar basalt- 

 sheets form other flat-topped ridges and outlying hills. 



Some 20 miles to the north the volcanic rocks 'die out, and the 

 country is then gently undulating and composed of fine red sand- 

 stone. At the Eembesi the schists of the gold-belt, named after 

 that river, crop up and are exposed for a width of 4 miles. Sand- 

 stones again come in, and continue to the Bubi Eiver, where basalts 

 (interbcdded with fine red sandstone) are once more to be seen, the 

 underlying sandstone-bed being indurated and much cracked, and 

 the fissures infilled with white silica, while the overlying sandstone 

 shows no alteration. Some of the lava here is highly vesicular, 

 and is studded with amgydales. On both the Bubi-Biver and 

 Gwampa slopes of the watershed the upper sandstone has been re- 

 moved, and basalt forms the capping of the flat-topped foot-hills. 



The Shangani Eiver has denuded a valley some 1500 feet lower 

 than the altitude of Bulawayo, and runs in a plain of alluvium from 

 half a mile to 2 miles wide. From that river onward the pre- 

 dominant rocks are still red and yellow sandstone, covered with open 

 forest, until, at 170 miles from Bulawayo, the undulating country 

 stops short with an abrupt descent of 400 or 500 feet to the level of 

 the Matobola Plains. This sudden drop is caused by an escarpment 

 of coarse red, incoherent sandstone, containing subangular pebbles of 

 jasper, banded ironstone, quartz, etc., Avhich either occur in irregular 

 layers or scattered singly or in groups throughout the grit. 



This escarpment begins many miles away to the south-west. It is 

 even a feature on the main road from Bulawayo to the Wankies 

 Coalfield, 00 miles distant, and runs in a broken line north-eastward, 

 making the Gololo, Domwe, and Guramina ranges, then continuing 

 round the headwaters of the Sesami and Bume Elvers (60 miles 

 to the east : see PI. XIX, fig. 2), whence it is noticeable in broken 

 bluff's away to the north-east near Gorodema's Kraals, until it seems 

 to merge with the Mafungabusi Mountains. 



The breaks in the precipitous cliffs are where rivers, such as the 

 Gunyanka, Senka, Sengwe, Bume, and Sesami, flowing from the 

 southern plateau have eroded gently -sloping valle}'s in the friable 

 rocks; but these interruptions make the general line more noticeable, 

 and give a bolder appearance to the perspective of receding bluffs. 

 The escarpment is made more prominent by the strip of flat country, 

 from 5 to 14 miles wide, known as the Matobola Plains, which 

 extend along the whole course of the base of the range. Until 

 this escarpment is reached, the sandstones (where cropping out in an 

 unweathered state) exhibit no dip, but in the cliffs the beds first 

 show a slight inclination to the south. 



