Yol. 70.] MIOCENE OE THE VICTORIA NTANZA, ETC. 149 



A specimen of rock taken a little farther on, within the Kuja 

 •Gorge (PL XXIII, tig. 1), just before one comes to the dolerite 

 itself, helps to explain the original character of these decomposed 

 schists. An outcrop of a very compact pale-grey rock, Avith a strike 

 of north by west, occurs at a distance of a mile (measured trans- 

 versely to the strike) from the schist at the ford. It is a spherulitic 

 quartz-porphyry, 1 which has undergone some crushing and altera- 

 tion, becoming a so-called sericite-porphyroid. Perhaps the 

 schists of the Kuja Ford are to be regarded as the marginal 

 and more extensively-crushed modification of the original quartz- 

 porphyry, with the usual increase of sericite, or as the crushed tuffs 

 of the quartz-porphyry. The actual contact of the dolerite-sill 

 Avith the ancient quartz-porphyry could not be observed, OAving to 

 the thickness of red soil. 



In order to make an examination of the quartzite south of 

 the Kuja Gorge at Vinyo, I ascended the rounded slopes of the 

 dolerite extending up to the precipices of the Avell-bedded quartzite, 

 Avhich is 500 to 600 feet thick. Although I searched diligently 

 for fossils, it Avas a fruitless task ; but the exposures of bare rock 

 Avere so numerous along the edge of the escarpment, and the section 

 from the base of the cliff up to the summit Avas so readily 

 accessible, that I could hardly have failed in my search if any 

 fossils had been present. The rock is, on the Avhole, veiy uniform, 

 consisting of Avell-bedded quartzitic sandstone, Aveathering in large 

 slabs, Avith streaks of haematite along the bedding-planes and joints. 

 Half Avay up the cliff I collected a piece of a slab shoAving sun- 

 cracks ; ripple-marks were abundantly present at all leA^els, and 

 occasionally impressions of raindrops and Avorm-tracks Avere visible. 

 Current-bedding is preA-alent, and sometimes there is a zone of 

 a fine conglomerate containing quartz-pebbles (up to § inch in 

 longest diameter). The dip varies here from 5° to 10° Avest-south- 

 westwards, and the prevalent direction of the ripple-marks Avas 

 Avest- south- Avest wards and east-north-eastwards, indicating a 

 gentle current from the south- south-east ; but I also observed the 



1 The rock is pale grey, compact, but slightly schistose, somewhat waxy 

 in lustre, and contains a few scattered, small, grey quartz-grains. Under the 

 microscope the quartz-phenocrysts present all the usual characteristics of 

 atypical quartz-porphyry : as, for example, the corroded and lobed appearance 

 and the inclusions of ground-mass (now altered to fine aggregates of white 

 mica) ; the quartz encloses an occasional flakelet of biotite, and shows strain- 

 shadows ; a hexagonal cross-section is present. Tourmaline occurs in a 

 few thin, pale indigo-blue strings, showing some parallelism and in one case 

 bordering a quartz-crystal. Under crossed nicols the ground-mass (but 

 slightly dusky in comparison with the quartz-crystals) is resolved into a 

 mosaic of mutually interfering spherulites, considerably cracked, and show- 

 ing tiny flakelets ofsericitic mica along the innumerable cracks ; even the 

 f elspathic portion seems to have altered into quartz and sericite. While most 

 of the spherulites are greatly shattered and cracked, a few are comparatively 

 intact, with white mica sweeping round them. Sericitic aggregates also 

 occur in strings between spherulites, and probably represent some of an 

 originally glassy base. The radial selvage enveloping a corroded quartz 

 extinguishes simultaneously with it, and in optical continuity. 



