204 ME. G. W. LAMPLTTGH OK THE [May I907, 



their capping after erosion had already greatly lowered this par of 

 the country. They are some 400 feet lower than the place already 

 described (p. 199) on the rim of the Matetsi valley, 7 or 8 miles to 

 the north-westward, where very similar surface-rocks were observed ; 

 and we cannot therefore regard these surface-beds as forming part 

 of a once-continuous sheet of ' Botletle-Schichten.' Moreover, I 

 found the same kind of material to be plentiful at still lower levels, 

 in the banks and dry bed of the Gongobujo River which drains 

 eastward to the Zambezi on the northern side of Logier Hill. 



The sections in the banks of this stream, 2 to 3 miles above its 

 mouth, showed much white ' calcrete ' and ' silcrete' — sometimes in 

 soft sintery banks of 15 to 20 feet — along with masses of a hard 

 splintery green rock, partly silicified (see Appendix I [F 1046, 

 p. 211]), and some red jaspery streaks; and material of this kind 

 was found to characterize the places where the gradient of the 

 stream was low, being generally absent where the stream flowed 

 steeply over the basalts. 



These deposits therefore sustain the conclusion previously stated^ 

 that the surface-rocks have been formed on the flats at different 

 stages in the lowering of the valleys, and that in this part of the 

 country they do not mark any definite period. 



Some further details with regard to the surface-accumulations 

 of the region will be found in Appendix III (p. 213). 



Lateritic Material. 



In places where the basalt is bare, or nearly so, the surface is 

 sometimes littered with rough irregular lumps of ferruginous grit 

 ( ; ferricrete '), due to the segregation of iron from the decomposing 

 rock; but I did not light upon any place where this material 

 formed masses comparable to those of siliceous and calcareous 

 composition described above. The same segregative process is 

 probably indicated by the occasional presence of thin cakes and 

 narrow strings of iron-ore on the rock-surface and in joints and 

 crevices of the basalt. I noticed these small iron-filled crevices 

 in several places, particularly in a dry kloof on the ridge 5 or 6 

 miles north-east of Matetsi, where the ore had been dug by the 

 natives and smelted in the adjacent forest, the relics of their old 

 bloomeries still remaining. 



The pellety lateritic soil of the plateau has been previously 

 described (p. 170). 



Fluviatile Deposits. 



The paucity of pebble-gravel along the bed of the Zambezi and 

 its tributaries is remarkable. On the unbroken plateau this may be 

 explained by the very low gradient of the streams; and in the 

 rejuvenated valleys the force of the water is, perhaps, too great to 

 allow such material to lodge. But it seems rather as if the basalt- 

 blocks, when once broken into fragments, are soon completely 

 disintegrated. Thus, within the Batoka Gorge, the river at low 

 water is generally fringed on both sides by a forbidding border of 



