Summary of Geological Observations. 
It supplies the building material adopted for the structures of European 
type at Entebbe, Mitiana, and other places. Its chemical composition is very 
constant, containing a percentage of Fe 20 3 , which varies from 51 to 55 per 
cent. ; hence it differs from that of the limonite nodules, w-hic-h are found 
in laterite, in which the percentage of Fe 20 3 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 (bog 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 part represented by quartz, hyaline (glassy), granular, 
or jasproid. I rarely noticed nodules or fragments of gneiss, or of palseozic 
rocks. So great at times is the abundance of quartzose 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 parts of Uganda, but constitute elongated hills with levelled 
summits, divided one from another by deep fissures, or else they 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 Entebbe 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 palaeozoic 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 inner 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 
2 c 
385 
