520 PROFESSOR J. W. GREGORY. 



quartzite (No. 227). The quartzites in this district appear to belong to two different 

 categories. The older quartzites which have a high dip and are interstratified with 

 the gneisses belong to the Bailundo Schistose Quartzites, while the higher ground 

 along the divide is formed of the Huambo Quartzites. 



After passing the head of the Cubango the route lay westward over biotite-gneiss 

 with irregular foliation ; and the appearance of a bold tor at Candumbo, about 1 1 

 miles to the west, warned us of our approach to the granite belt. About 7 miles 

 before reaching Candumbo, at the head of a deep tributary to the Queve, we passed 

 a band of cordierite-hornfels with its foliation striking to the north. The country 

 between Candumbo and Huambo is composed mainly of granite ; there are numerous 

 exposures beside the track and in high tors to the south and north. One of them 

 we called Chichester Cathedral, from the resemblance of an isolated monolith beside 

 it to a detached belfry ; this mass consists of a coarse-grained biotite-granite. 



Hua.m6o 



CuhmaJiala. 

 Valley 



Fig. 8. 



Near Huambo the granite extends on both sides of the track, which crosses a 

 long strip of a white friable sandstone composed of quartz grains in a felspathic 

 base ; and the relations of these rocks beside the Culimahala River show that the 

 granites were once covered by a widespread sheet of arkose due to their decom- 

 position (fig. 8). 



The streams that flow northward have deep rocky gorges, while those to the south 

 lie on the floor of wide shallow valleys ; this contrast shows that the northern 

 streams, which discharge to the Atlantic, are extending inland and thus encroaching 

 on the Zambesi basin. 



III. The Correlation of the Benguella Series. 



The rocks seen in Benguella may be divided up into five groups : 



(1) Pleistocene deposits, including drifts, alluvial deposits, sand dunes, lake beds, 

 the sands on the Bulu-Vulu, the calcareous tufas of Ochilesa, laterites, etc. 



(2) The Mesozoic rocks of the coast zone. 



(3) A series of old sedimentary rocks widely spread on the surface of the plateau. 



(4) Gneisses, schists, and granitic rocks, which form the foundation of the whole 

 country. 



(5) Various lavas, and intrusive rocks of undetermined age. 



