Geology of the Ningi Hills, Northern Nigeria. 437 



Filani a broad outcrop of a remarkably fresh gabbro dyke (107) 

 exposed for a width of some 40 to 50 yards, forms a low ridge 

 striking east and west. This was the only basic intrusion 

 encountered during the traverse. At Keffi Filani there is a small 

 outcrop of a somewhat granulitized, gneissose granite (108, 110), 

 which is different in character both to the Sabon-Garri and the 

 Ningi granites. Only two exposures were observed, one forming 

 a few isolated knobs and the other forming a low ridge running 

 east and west. This granite appears to be intermediate in age 

 between the typical granites. It appears to be intrusive in the 

 Sabon-Garri granite, but has been crushed as a result of the move- 

 ments that accompanied the intrusion of the Ningi massif. No 

 contact with the Ningi granite was observed. 



The Ningi Granites. 



North of KeflS. Filani the Ningi granites are first seen in the valley 

 of a small stream that heads near Ka and flows south through Keffi. 

 The well-marked contact, with chilled edges, is at this point against 

 the old granites and gneisses. Travelling eastward towards Ningi 

 the track skirts a low range of gneissose hills (109), with bars of 

 harder, more siliceous rock (111), behind which rise the higher hills 

 of the Ningi granite. 



Ningi itself, lying securely behind triple walls at the head of a 

 small valley, was formerly the chief village and fort of a Pagan 

 tribe who conducted an extensive and profitable trade in slave 

 raiding. The " new " granites come in about 1\ miles north of the 

 village. The contact is clearly marked (113, 114). At the point 

 traversed the Sabon-Garri granite forms large, flat, bare sheets (112) 

 or slightly convex turtle backs, and the newer granite rises steeply 

 and displays a certain horizontal jointing that resembles dry walling 

 on a Cyclopean scale. The Ningi granite (115) is a riebeckite granite, 

 and is similar to the granite forming the Kila and Fagam massifs. 



A large dyke, or series of parallel dykes of a dark-green rhyolite, 

 starts at Ningi and runs north-easterly through the villages of 

 Ari and Teffi. At Teffi the dyke channel is occupied by porphyries 

 as well as rhyolites (117, 118), whilst porphyries (138) and segirine- 

 rhyolites (139) are exposed between Wurji and Guaram. 



Between Ari and Teffi these dyke-rocks have resisted denudation 

 more than the surrounding granites and gneisses, and stand out 

 boldly, forming the southern wall of the hills. Passing north-east 

 towards Wurji they form numerous isolated grassy hills and low 

 ranges. A quartz-riebeckite syenite occurs at Teffi, lying apparently 

 in contact with the Ningi granites and the porphyries (119, 120). 

 At the crossing of the Delimi between Teffi and Wurji orthophyre 

 (121) and porphyry (122) are exposed in the river bed, and exposures 

 occur in the hills north of Wurji (123). 



The syenites reappear at Guaram, where they form several low 

 hills lying near to the town (129). The contact rocks in the north- 



