440 Major G. W. Williams — 



Limncea (sp. 1). In the alternating sandy layers fragments of 

 Bulimus (sp. ?) are sometimes found. 



The valleys opening out of the hills, especially those facing north 

 or north-east, are usually deeply filled with light, sandy soil, partly 

 detrital and partly seolian in origin, which forms a level floor to the 

 valley. A remarkable feature is the uniform absence of water- 

 courses in these valleys. The rainfall, averaging 35 to 40 inches, 

 falls mostly in a few torrential downpours during August and 

 September. The rains pour down the bare granite catchments into 

 the valleys, but sink through the soil and do not form water- 

 courses. The whole country becomes waterlogged, and the few 

 river beds that traverse the plains (mere grass-grown depressions) 

 indicate the general direction in which the surface waters move 

 towards the main course of the Delimi and Hedaji rivers. In the 

 floods the Delimi overflows its low banks and spreads, many miles 

 wide, across the planes. The country is very similar to the Cooper's 

 Creek country of Australia, where one may perish of thirst one 

 day and the next, 10 mile wide rivers pouring down from the 

 Diamantina and Georgina country bear the Queensland flood 

 waters to the lakes of South Australia. Water level in the dry season 

 varies considerably. In the neighbourhood of the hills it varies from 

 6 to 12 feet, but in the plains increases to 40 feet. Further north- 

 east the depth increases to 120 feet in Bornu province. 



Parallel to the Delimi River are a series of long, narrow, deep 

 lagoons, often surrounded by permanent swamps. Near to Guaram 

 is a lagoon 1^ miles long, 250 yards wide, and 15 to 20 feet in depth. 



Laterites. 



The horizontally bedded layers of vesicular ironstone that are so 

 characteristic a feature of the topography of the Bauchi Plateau 

 and which are found throughout the country between Delimi and 

 the Ningi Hills are not developed in the light soils east of the Kila 

 and Fagam Hills. In the immediate vicinity of the Kila granites 

 certain bands of sand carry concretions of ironstone, but uniform 

 lateritic sheets are lacking. 



The Occurrence op Tin in the Area. 



The younger granites of the Bauchi plateau, which are similar to 

 and probably contemporaneous with the granites of the Ningi 

 type, are well known for the tin contained in the streams draining 

 from them. This reconnaissance, however, definitely establishes 

 the fact that the Archaean granites of the Sabon-Garri type are also 

 stanniferous. From Chow to Yarde Gongome all streams that drain 

 these granites carry more or less tin in the wash, and relatively large 

 quantities are found in the surface soils in the vicinity of lodes such 

 as those in the neighbourhood of Yarde Kerri. 



Near to Bongwelli a pegmatite stockwerk in Sabon-Garri granite 

 sheds a large quantity of tin into the Dada Howa creek (a Delimi 



