504 PROFESSOR J. W. GREGORY. 



selenite. I could find no fossils in this gypsiferous bed, but saw no evidence why it 

 should not be included in the lower part of the Cretaceous Series. 



The correlation of the Cretaceous beds is considered on pp. 521, 522. 



B. Benguella to the Upper Catumbella River. 



At the city of Benguella the railway turns inland and goes south -south-eastward 

 over a wide alluvial plain in the valley of the Cavoca River. The Cretaceous rocks 

 are seen in the distance on both sides of this valley. At Bimbas Road Station two 

 wells were sunk through the beds on the floor of the valley to the depth of 56 and 

 7G feet * ; they passed only through sand. 



South of Bimbas Road a cliff of conglomerate can be seen to the east of the 

 railway, which passes between hills of gravel and coarse conglomerate ; the latter 

 contains blocks of gneiss, granite, and schist. The boulders are as much as 4 by 3^ 

 by 1\ feet in diameter, and they are well rounded and embedded in coarse sand. These 

 beds were clearly deposited as torrential fans at the foot of the gneiss hills to the 

 east. This boulder bed passes gradually upward into sandstone. Mr Robins had 

 seen no fossils in these rocks, and their age is uncertain. They may belong to the 

 lowest part of the Cretaceous Series or may represent part of the Dombe Sandstone, 

 which Choffat includes in the Cretaceous, but has been also assigned to the Lower 

 Mesozoic. 



The conglomerate and sandstone end inland against hills of ffneiss, which is well 

 exposed in the Lengwe Gorge. Although the edge of the plateau has been cut away 

 in the Lengwe valley, even there the slope is so steep that the railway ascends by 

 rack work, which begins at 380 feet (at km. 5f8) t and ends at 790 feet (km. 54). 

 The gneiss is well seen on the banks of the gorge and in the cuttings along the 

 railway. The most characteristic rock is a coarse, well-foliated biotite-gneiss, which 

 is mostly gray or dark bluish in colour. Pink bands also occur. Some of the rocks 

 show an augen structure and wisps and clots of biotite.- The foliation is often con- 

 torted. Some of the layers are hornblendic gneiss. Some varieties contain biotite 

 in excess and pass into coarse biotite schists. The gneiss is traversed by quartz- 

 felspar veins, some of which are coarse pegmatites with large biotites. In others 

 there is no biotite, and but little felspar ; so they pass into quartz veins, one of the 

 largest of which is beside the second viaduct. Some of the intrusive veins show well- 

 developed graphic structure. 



The gneiss is often broken by faults, of which the most typical are small parallel 

 thrust planes that are nearly horizontal. In one case, at km. 50^, four such faults 

 occur in a height of 12 feet ; the upper side has been moved to the north-west. 



- One of them was at first, a Mowing well. Both at first gave good water, but after heavy rains all the water 

 in. in the deeper well became too charged with magnesia to he of use ; and though this well was several times pumped 

 dry, tin- water never recovered its original good quality. 



I The kilometre distances are those along the railway from Lobito. 



