Geology of the Ningi Hills, Northern Nigeria. 439 



aplitic veins (137) were observed to the south.- west of Fagam, but 

 the actual contacts were covered with superficial accumulations. 



The Intrusive Rocks op the Area. 



With the exception of the gabbro dyke near Keffi Filani all the 

 intrusives are acid in character. The gabbro, which is exceedingly- 

 fresh, is probably referable to the mid- Tertiary period of volcanic 

 activity, of which one important focus existed near Burrin, some 

 140 miles to the north-west of Ningi. The characteristic intrusions 

 in the Sabon-Garri granites are rhyolites and aegerine-riebeckite- 

 porphyries. Rhyolites, soda-rhyolites, and porphyries form a 

 broad belt extending from Ningi to midway between Wurji and 

 Guaram, and, judging by " floaters ", the belt passes in an easterly 

 direction near to the village of Duchi, a few miles south of Guaram. 



Syenites occur in close proximity to the rhyolites at Teffi and at 

 Guaram. In some cases the rhyolites are intruded into the 

 porphyries. Dykes of quartz-felspar rock, very hard and resisting 

 weathering well, are frequently encountered in both the gneisses and 

 the Sabon-Garri granites. No. Ill is typical of this rock, which 

 often forms " bars " across the hill rivers. 



Rock Succession in the Area. 

 The following table indicates the general succession as observed 

 during the traverse : — 



Pliocene and Posl-Pliocene . ^olian sands. 



Lacustrine sands and clays. 

 Tertiary (1) . . . Gabbro dyke. 



Mesozoic .... Ningi-Kila-Fagam granites (Ningi 



type). 

 Ningi-Wurji rhyolites. 



„ porphyries. 



Ningi-Guaram syenites. 

 ? . . . . Keffi Filani granite. 



Archman f ^girine-Riebeckite porphyries. 



\ Banded rhyolites. 

 Riebeckite Granites — Sabon-Garri type. 

 Gneisses and other crystalline rocks 

 forming basal series of Northern 

 Nigeria. 



Surface Accumulations and Drainage. 



North and north-east of Ningi the soil is markedly seolian in 

 origin. During the traverse a number of test pits were sunk in the 

 valleys of the Kela and Fagam Hills and in the drifts along the edge 

 of these massifs. These pits almost invariably disclosed a sequence 

 of light sands, largely wind-blown in origin, and grey or whitish 

 clays, flocculent in water, and containing fine, wind-blown sand.^ 

 The clays appear to be lacustrine in origin. Near Fagam a pit sunk 

 at the edge of the granite yielded a layer of marly clay at 12 feet 

 ^(water level), which contained decomposed fragments of a shell of 



^ Cf. The Geography and Geology of Northern Nigeria, pp. 215 et seq. 



