508 PROFESSOR J. W. GREGORY. 



beside a spring in the valley of Bandionhime. The water of this spring has been 

 bottled and sold in Benguella as a mineral water ; but its value appears to depend 

 on its remarkable purity. The spring flows from the quartzites, which there strike 

 to *_ >( .)0° and dip from 15° to 20° northward. The quartzites extend from Ferreira's 

 to Babaera, where they are well exposed beside the waterfall. The rocks there dip 

 35° to the north of north-west. To the west of Senhor Pire's farm the rocks dip 40° 

 west and strike to nearly due south. The rocks are coarse-grained quartzite grits, 

 containing many fragments of felspar ; and the rock has obviously been formed from 

 the waste of the granitic rocks. These quartzites are considerably altered, for they 

 contain authigenous muscovite (PI. II, fig. 2), lines of authigenous epidote, and 

 inclusions have been developed in the quartz along lines which are continuous across 

 adjacent grains. These rocks are associated witli banded cherts, which under the 

 microscope prove to be silicified rhyolites. To the east of these quartzites, and 





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Fig. 5. 



apparently overlying them, are volcanic rocks which form most of the central part 

 of the Oendolongo Hills. A sheet of columnar rock above the third stream west of 

 Cruz's can be recognised from the railway, but I had not time to reach it. A 

 sheet of rhyolite tuff is exposed at intervals from just east of the Agricultural 

 Station of Quingenge, westward along the foot of the hills ; it rests there upon 

 the granites, which outcrop over the plain to the north of the hills and can 

 be seen in some of the gullies. The tuffs east of Quingenge Agricultural Station 

 consist of fairly coarse fragments ; but further west the rock is very fine-grained 

 and compact, so that in hand specimens I was doubtful how much of it was tuff, 

 for some of it might have been a felspar-porphyrite. Mr Tyrrell's microscopic 

 examination indicates that the whole sheet is a rhyolite tulf. The rock in some 

 places, as close to the Agricultural Station, has been silicified and thus acquired a 

 greasy or horny lustre similar to that of some keratophyre. 



To the east of Quingenge a mass of pinkish fine-grained granite rises from beneath 

 the rhyolite tuffs. This rock can be followed for a couple of miles east of Quingenge, 

 and rises to a considerable height on the hills. This fine-grained granite is succeeded 

 eastward by the sandstones of the eastern part of the Oendolongo Mountains. 



