ORIGINAL ARTICLES. 



Preliminary Notes on the Geology of the Ningi Hills 

 Northern Nigeria. 



By Gerard W. Williams, D.S.O., M.C., M.I.M.M., F.G.S. 



WITH PETROGRAPHICAL APPENDIX BY R. H. RASTALL, M.A., 

 M.I.M.M., F.G.S. 



rPHE country described in the following notes comprises the 

 -"- area lying between latitudes 10° N. and 11° 30' N. and longitudes 

 8° 45' E. and 10° E., and is situated in the northern portion of 

 Bauchi province and the south-eastern portion of Kano province, 

 Northern Nigeria. 



The Delimi Eiver runs diagonally through the area. This river, 

 one of the chief feeders of Lake Chad, rises on the main hydro- 

 graphic centre of Northern Nigeria. The three largest rivers that 

 rise in the Protectorate — the Delimi, Gongola, and Kaduna — have 

 their head-waters in a swampy, moorland plain that attains its 

 highest elevation of approximately 5,000 feet at a point midway 

 between Jos and Bukuru, near to the Rayfield Mines main camp. 

 The Delimi River flows through Jos and Narraguta, and then plunges 

 down the Narraguta Gorge below the native market. Thence north- 

 easterly through Rafin Jaki camp, Deriko, and Bongwelli to Lemmi. 

 Below Lemmi the river widens to 400 yards, and at Guaram it is 

 fully 1,000 yards wide. Thence the river flows past Kategum to 

 join the Hedaji River, and the united stream, then known as the 

 Yo River, winds deviously eastward to Lake Chad. The head- 

 waters above Narraguta drain the high land of the Bauchi Plateau, 

 and as both the main stream and its upland tributaries drain from 

 the stanniferous granite of the 'Ngell Massif the river washes are 

 all tin-bearing. The boundaries of this massif, on its northern side, 

 are practically continuous with the boundary of the Plateau from 

 Rukuba to Toro. Below the plateau the Delimi has been proved 

 tin-bearing for nearly 50 miles — as far as Lemmi. The bulk of this 

 tin is not derived from the stanniferous granites of the plateau, 

 but is fed to the main stream by tributaries draining the rugged 

 group of ranges known as the Jengre Hills, of which the Buji Peak 

 forms the highest point. The Narraguta Gorge is excavated through 

 a series of gniesses and other ancient crystalline rocks, and the bed- 

 rock of the river as far as Lemmi is almost exclusively composed of 

 gneisses. Below Biberi the valley widens out into a broad flood 

 plain, which attains a width of from 10 to 12 miles at Bongwelli. 

 From the floor of this valley rise numerous ridges and domes of 

 granite, which decrease in number as the river flows north-east from 

 Lemmi. From Lemmi to Lake Chad (with the exception of a few 

 isolated granitic hummocks) the flood plain widens out on to the 



