CONTRIBUTIONS TO THE GEOLOGY OF BENGUELLA. 509 



South of the Agricultural Station of Quingenge the Cambuacambula flows for 

 about 3 miles over the fine-grained granite, which is exposed owing to the 

 denudation of the tuffs. As the floor of the valley rises more rapidly up the hills 

 the rhyolite tuffs appear in blocks scattered over the granite. A mile further on 

 the granites are covered by a black rhyolite. I could not find the actual contact, 

 but saw the rhyolite within a foot or two of the junction ; and the rock showed no 

 trace of contact alteration and there were no tongues of granite entering it. Hence 

 the rhyolites appear to be younger than the granite. The path then rises steeply, 

 showing numerous exposures of rhyolite, some of which is vitreous and some has a 

 glomero-porphyritic structure. On weathered surfaces the banded structure is often 

 clearly displayed. These rocks continue to the top of the pass at the height of about 

 6500 feet ; and on the top of the hills on the eastern side of the pass (6670 feet) it is 

 clearly a banded rhyolite with conspicuous phenocrysts of quartz. The red sandstones 

 also occur near the top of the pass, which commands a fine view southward over a 

 large basin ; the outlet to the Catumbella River is through a gorge at the south-western 

 end. A kopje, obviously of granite, occurs on the floor of the basin at 212° from the 

 pass. The basin is bounded to the west by hills which appear to be the continuation 

 of the quartzites of Babaera. 



The central part of the northern face of the Oendolongo Hills, therefore, consists 

 of a thick series of rhyolites resting on a rhyolitic tuff, which is itself underlain by 

 the normal granites of the district. The rhyolite series is overlain by a thick series 

 of red and white sandstones. The western part of the hills is composed of white 

 altered quartzites, with some authigenous micas, associated with cherty banded 

 rhyolites. The fine-grained pinkish granite east of Quingenge may perhaps be 

 younger than the main series of granites, but I saw no evidence to connect it with 

 the rhyolites. 



West of Cruz's store an olivine-basalt dyke cuts through the granite and probably 

 continues into the tuffs. 



D. From Lepi to Huambo. 



Near Lepi (km. 367, 5371 feet) the railway enters a new type of country different 

 from any seen between that station and the coast. Between Lepi and the granite 

 hill to the west at Old Lepi (km. 355, 4783 feet) is an area of deep chocolate-red 

 soil which is due to a sheet of olivine-dolerite that is exposed in the railway cuttings. 

 This rock is doubtless intrusive, since a coarse quartzose sandstone beside it is 

 extremely decomposed. The sandstone belongs to a series of old sedimentary rocks 

 which extend eastward to the Kunhungamua valley ; they may be grouped and 

 named after their most characteristic rock, the Lepi graywackes. The railway on 

 leaving Lepi climbs by a very sinuous route up the Chicanda valley on to the summit 

 of one of the highest of the Benguella plateaus. The rocks are well exposed in the 

 numerous railway sections, and they include graywackes, quartzite, cherts and slates, 



