CONTRIBUTIONS TO THE GEOLOGY OF BENGUELLA. 519 



which strikes to 132°. Journeying thence north-westward the track crosses a hill of 

 quartzite and descends to the deep valley of the Umbal, the banks of which consist 

 of massive gneiss with obscure foliation. This rock is bounded on the western bank 

 of the river by a hornfels-like rock which Mr Tyrrell has determined as a granulitic 

 amphibolite. The strike of the gneiss is here almost due north and south, and on 

 the margin of the gneissoid rock are many basic segregations or inclusions. The 

 gneissoid rock is then probably intrusive into the amphibolites ; but I failed to find 

 any indications of contact alteration in the sandstones, which overlie the crystalline 

 rocks on the western slope of the valley. It appears probable that this sandstone is 

 a younger rock resting on the gneiss and schistose quartzites. 



(3) The Umbal to Huambo. — -From our camp on the Umbal we marched in a 

 westerly direction to the railway, which had now been extended as far as Huambo. 

 The route for the first 6 miles was westward over quartzites and a plateau which 

 had part of the character of the Bulu-Vulu, though the grassy plains were narrow 

 and were bordered by woods. After marching 6 miles the track turned south, to 

 keep along the high ground around the head of the Cutato valley, and after about 

 4 miles in this direction we came on exposures of cherty, coarse, white quartzites. 

 After another 2 miles we saw some bosses, obviously of gneiss, down the valley 

 to the east-north-east; but the route still lay over quartzites, and we continued - 

 on them for about 6 miles, after reaching a waggon road which had been opened 

 from Belmont to the railway head. Blocks of gneiss appeared from beneath the 

 quartzites, and about a mile further on, in a shallow valley to the north of the 

 road, is a water-hole due to a bar of hornfelsed felspar porphyry with abundant 

 scapolite (No. 199). 



I had not time to visit the Chingwari Hills, which may consist of either quartzite 

 or of hornfelsed porphyry, which occurs to the north as well as to the east of them. 

 At the northern foot of the Chingwari Hills is an extensive plain known as the Little 

 Bulu-Vulu, which appears to be due to a sheet of gray marls and sandstones, of 

 which exposures occur due north of the summit of Chingwari. We continued over 

 this Little Bulu-Vulu for about 6 miles, an occasional valley showing exposures of 

 white quartzite and pebbles of sandstone. To the west of the Bulu-Vulu plain are 

 numerous exposures of quartzite containing grains from one-eighth to one-sixteenth 

 of an inch in diameter. At the head, however, of the Cubango, one of the north- 

 western tributaries of the Zambesi, we again entered an area of gneiss. Most of it is 

 the normal gray biotite-gneiss, but it includes some dark gneiss with obscure foliation, 

 and some intrusions of a felspar porphyry. Travelling along the watershed to the 

 west of the head streams of the Cubango we passed again for about 3 miles over 

 some coarse white quartzite, and then a large boss of a fine-grained gray biotite-gneiss 

 with a foliation of 48°. Close beside our camp, in a picturesque group of gneiss crags, 

 we crossed a bar of schistose quartzite, which strikes to 43° ; and on the higher 

 ground above it was a considerable exposure of a coarse granular- sedimentary 



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