Smnmarv of Geological Observations. 



It supplies the Ituildiiig niateriul ;i(lopte<I fur the structures of European 

 type at Entehbe, Mitiana, and other phxces. Its chemical composition is very 

 constant, containing a percentage of Fe 2O3, which varies from 51 to 55 per 

 cent. ; hence it differs from that of the limonite nodules, which are found 

 in laterite, in which the percentage of Fe 2O3 may be as high as 82 per cent. 

 In this region the limonite forms several rising grounds, some over 300 feet 

 above the present level of the lake. As to its origin, I believe it was deposited 

 in the bed of the lake, at a time when it was far more extensive than at present, 

 as is evident from a whole series of indisputable facts, the decomposition being 

 effected by a mechanical process analogous to that which in lacustrine basins 

 originates the limonite (l)og ore) of marshy places. 



Hence, in my opinion, the concretionary limonite may be of great 

 importance, as serving to indicate the former limits reached by Lake Victoria, 

 of which even Lake Isolt, near Bujongo, may be merely a remnant. Similarly 

 the few patches of concretionary limonite met in the Butiti district may possibly 

 represent old extensions of Lake Albert. In the limonite are embedded 

 numerous stony fragments and nodules varying greatly in size. This detrital 

 material is for the most jDart represented by quartz, h3^aline (glassy), granular, 

 or jasproid. I rarely noticed nodules or fragments of gneiss, or of palaeozic 

 rocks. So great at times is the abvmdance of cpxartzose nodules or fragments 

 as to give rise either to conglomerates or else to breccias with limonitic cement, 

 as the case may be. 



The scenery of the limonite region is typical in the form of its rising 

 grounds. These do not present rounded contours, such as are normally 

 observed in other j^arts of Uganda, l)ut constitute elongated hills with levelled 

 summits, divided one from another by deep fissures, or else thev stand isolated 

 on the plain, representing the remains of what at other times must have been 

 the unbroken surface of the ground. In this respect the Entebl)e and Mitiana 

 districts are characteristic. 



The laterite resulting from the transformation of the felspar rocks, under 

 the action of the atmospheric agencies, aided by the high temperature and by 

 the alternating droughts and heavy rains, may be said to form the surface layer 

 of the ground throughout this region. It is found not only in the gneiss and 

 granite zones, but also where the paleeozoic occurs and forms on the rocks 

 in situ a covering of various thickness, which may in places acquire quite an 

 exceptional development. Characteristic is always the iinier red colour, which 

 is due to the excessive oxidation of the numerous iron ores that we have seen to 

 be present in those rocks. 



In the laterite is often noticed an abundant micaceous hematite, which in 



385 2 c 



