510 PKOFESSOK J. W. GREGORY. 



and some interbedded rhyolite tuft's which arc blue-hearted when fresh but turn gray 

 when weathered. The volcanic rocks arc less abundant than in the Oendolongo 

 Mountains, and I saw only tuffs and none of the rhyolitcs themselves. 



The most typical rocks of this series are a black, fine-grained cherty graywacke, 

 which in the field I recorded as chert. One variety (No. 130), from a spur east of 

 Lepi and about a mile west of the locality known as Homer's Camp, appears in a 

 hand specimen to be a banded cherty quartzite ; under the microscope it proves to be 

 a fine-grained graywacke ; the larger grains of quartz range from about a tenth to a 

 quarter of a millimetre in diameter ; the grains are angular, and include a little felspar, 

 some of which is oligoclase, and white mica. The rock shows an imperfect cleavage, 

 the particles having been to some extent rearranged by pressure. A graywacke 

 (No. 131) on the spur to the east of the last specimen is also fine-grained, but the 

 rock is more massive ; it is not cleaved, and the banding is faint ; to the west of the 

 cherty graywacke (No. 130) the rock may be described as an indurated siliceous 

 mudstone. The series includes some slates. 



The prevalent dip, in spite of some folds, is to the east, so that the rocks nearer 

 Homer's Camp and in the steep ascent to Calenga are higher in the series than the 

 graywackes nearer Lepi. These higher rocks are mainly quartzites ; in fresh 

 specimens the fracture passes through the grains as readily as around them, and 

 specimens in which this does not happen (i.e. the sandstone beside the olivine-dolerite 

 west of Lepi) are probably decomposed quartzites. 



The graywackes near Lepi are only imperfectly cleaved ; but further east the 

 rocks are more altered, and some show an incipient foliation. This feature is well 

 marked in a greenish quartzite (No. 135) from near Homer's Camp. The rock was 

 identified in the field as an epidotic sandstone ; under the microscope it proves to be 

 an altered graywacke ; the original quartz grains show undulose extinction, and the 

 borders have been occasionally altered to a granular mosaic ; the base has been 

 recrystallised as secondary quartz, abundant granular epidote, and prisms of 

 clinozoisite. The epidote has been formed along irregular lines, and has thus given 

 rise to an incipient foliation. 



The Lepi Series is intersected by intrusions of dolerite. Some of the dykes and 

 the slates which they intersect are intensely decomposed, and at about km. 379^ 

 they have been altered to a china clay, probably by pneumatolytic action. Close 

 beside the china clay are exposures of decomposed pink clay. Two kilometres further 

 are exposures of blue cherty graywacke and variegated slates, which have been bent 

 into occasional shallow folds. 



This varied series forms the great dissected plateau which includes the mountain 

 of Holocasa (7848 feet) to the north of the railway, and the range known as the Serra 

 Corvo Andrade, which extends from the railway south-south-westward across 

 Benguella to the province of Mossamedes. The sedimentary structure of this 

 country is well seen in many views near and east of Calenga. Thus the footpath 



