148 de. f. Oswald ox the [June 19 14, 



(4614 feet), a yellow-brown sand prevails, with frequent stretches 

 of old river-gravel containing large quartzite pebbles, and patches 

 of murrain often occur in which these pebbles are sometimes 

 embedded. 



The plateau stretches far to the northward, but is dominated on 

 the east by the lofty quartzite-escarpment, trending north-north- 

 west and south-south-east, of the Kisii Highlands. This cliff rises 

 1500 feet above the level of the old peneplain, and stretches far 

 away to the south-south-east ; while on the north-north-west it 

 ends in the bastion of Itumbe. still 6000 feet above the sea. The 

 upper edge is precipitous, but the lower slopes show here an 

 inclination of only 35°. The low rounded foothills at the base of 

 the white quartzite-cliff are composed of a dark-green, very fine- 

 grained dolerite, 1 forming a sill which has insinuated itself 

 between the gneissic basement and the cover of quartzitic sand- 

 stones, changing the latter near the contact into snow-white 

 quartzite — a conspicuous zone of colour in the face of the 

 escarpment. The underlying dolerite weathers deeply to a thick 

 red clay, which is very fertile, and hence determines the situation 

 of the numerous settlements of the Kisii people. It forms the 

 belt of lower ground, not only at the base of this Yinyo escarpment, 

 but also within the deep gorge of the Kuja River, which has cut 

 its way through the quartzite-plateau. The dolerite-sill comes 

 also to view along the floor of the upper course of the Kuja within 

 the area of the Kisii Highlands. 



Skirting the western base of the escarpment, I crossed the Kuja 

 again by a ford at the altitude of 4441 feet : that is, only 94 feet 

 above the level of the river at the Sakwa bridge, 6k miles lower 

 down, thus revealing a very gentle gradient for this part of its 

 course. The rock is here an extremely-rotten sericitic chlorite- 

 schist, 2 with foliation directed 60° south-south-westwards, and it 

 was difficult to obtain even a moderately-fresh specimen. 



1 The rock consists of a fine felt of laths of plagioclase (oligoclase-ande- 

 sine, AboAn 3 ), together with granular, very pale-brown augite. In a more 

 deep-seated specimen from the Vinyo Gorge the augite is subophitic, and has 

 become replaced by chlorite. Ihnenite has become completely altered to 

 leucoxene, and there is some interstitial chlorite, probably representing an 

 altered glassy base. Fine aggregates of small quartz-granules, with inter- 

 stitial vermicular chlorite, occur in irregular nests (especially along zones), and 

 have probably been derived from the absorption of the overlying quartzite. 

 The rock near the junction becomes full of amygdales of quartz (f inch or 

 less in diameter), either chalcedonic containing spherulitic chlorite centrally, 

 or else an aggregate of quartz-grains with a lining of chlorite. Other 

 amygdales may consist of a nucleus of pyrite surrounded by epidote, and 

 this in turn by chalcedony. Pyrite also occurs in irregular masses 

 bordered by haematite. Much-altered specimens of the junction-rock become 

 essentially a quartz-epidote rock with chlorite. 



- The schistosity of the greenish-grey rock with silky foliation-planes is 

 due to very fine flakes of sericitic mica and chlorite. The numerous 

 * eyes,' occurring down to small dimensions, are composed of very fine aggre- 

 gates of spherulitic chalcedony and chlorite, and are wrapped round 

 by chlorite and sericite. In some cases such aggregates show prismatic 

 outlines, as if pseudomorphous after felspar-crystals with their long axes 

 nearly normal to the foliation-planes. 



