Geology of the Ningi Hills, Nortliern Nigeria. 435 



far-stretching plains of wind-borne sands and superficial accumula- 

 tions that cover the bulk of eastern Kano and Bornu Provinces. 



The traverse on which these notes were made was primarily 

 undertaken as a prospecting tour. In consequence special attention 

 was paid to the hilly country, as the plains, owing to their uniform 

 covering of recent deposits, offer no exposures of the underlying 

 rocks. Starting from the main camp of the Bongwelli Mines the 

 route ran north through Chow and Sabon-Garri to the main camp 

 of the Yarde Kerri Group Mines. Thence easterly to the Minna 

 camp on the river of that name, and thence along the southern face 

 of the Ningi Hills. Skirting the western hills of the Ningi massif 

 the route ran over broad plains in a north-easterly direction to the 

 massif of the Kila Hills, which rise like a smooth-walled island from 

 the level plain. South-east of Kila the Fagam Hills were visited, 

 but only a portion of their granite was examined. The return 

 journey was made along the northern face of the Ningi Hills, and 

 thence back to Sabon-Garri. From this village the return route was 

 westerly to Rahama and back to Bukuru by rail. 



From Bongwelli to Chow the basal rocks are gneissose, but 

 exposures are few in number. The village of Chow lies at the foot 

 of a group of granite hills, which form a singularly perfect example 

 of platy desquamation. The domes rise sheer from the light soil, 

 the sides at the base being usually slightly concave and the domes 

 are perfectly rounded. The native name for this group of hills 

 means " breasts of a young woman ", and, as is often the case in 

 native names, the phrase is singularly appropriate. 



The Sabon-Garri Granite. 



This granite (100) ^ is coarse-textured with felspars (perthite) 

 up to an inch in length. The dominant ferromagnesian mineral is 

 riebeckite. It extends over a very wide area. For convenience 

 I have called it the Sabon-Garri granite, for it attains its largest 

 development between that village and the Ningi Hills. 



When Chow is left behind the country changes rapidly in appear- 

 ance, and west and north extends a wide area of rugged granite 

 ridges and domes. On the slopes of the valleys the thin surface 

 soil contains large numbers of felspar crystals derived from the 

 weathered granites. 



Three miles north of Chow a very large dyke of aegirine-riebeckite- 

 porphyry (101) forms a low ridge striking east-west, and numerous 

 smaller dykes of similar material are visible in the granites and 

 maintain the same general strike. Slight marginal chilling of the 

 dyke is usually noticeable. A few miles further north a series of 

 small dykes of devitrified rhyolite (102) are exposed in the valleys 

 lying between the granitic domes near to Taura village. 



At Tema, 5 miles south of Sabon-Garri, the typical granites are 



^ The numbers in brackets refer to specimens now deposited in the Sedgwick 

 Museum, Cambridge, and described in the appendix to this paper. 



