364 M. Fergusson — N'otes on Geologu of Tanganyika. 



proceed further north the felsite disappears, and at Mpimbwi occur 

 granite, gneiss, and schists. ["A specimen of gneiss or crushed 

 granite from this locality presents under the microscope a good 

 example of cataclastic structure with long irregular patches of 

 quartz (showing marked undulose extinction), some microperthite, 

 and bands of sericite in a mosaic of crushed quartz and felspar."] 



While at Kilando we experienced three earthquake shocks, only 

 a small interval of time elapsing between them. The missionaries 

 say they are of frequent occurrence, especially during the months of 

 September, October, and November. Here the plateau is broken 

 up, and the country descends in altitude to hills of 400 feet or 

 500 feet in height, with sometimes extensive plains and valleys. 



The occurrence of felsitic rocks on both sides of the lake suggests 

 that the rift had occurred through the middle of a large mass of 

 this rock which originally had been continuous, and that the lake 

 was formed subsequently. 



Recrossing to the western shore at Tembwi we find granite, gneiss 

 and schists with a large quantity of white quartz veins running 

 through them. Going north and approaching the Lukuga Valley 

 these gradually descend, breaking up into low ridges and hills, and 

 give place to deep red sandstones, which, however, are only of limited 

 extent and appear to be quite recent, as I found what I took to be 

 crab markings on the surfaces, and they were probably deposited 

 along a river valley. The river was evidently of much larger size 

 at one time, and even now is of considerable size during the time of 

 floods, as evidenced by the great width of the bed and the position 

 of native dwellings, which are all situated high up and back from 

 the banks. 



The only known deposit of limestone in the Tanganyika district 

 occurs at the French mission station Mpala, a few miles south of 

 Tembwi, It is a white crystalline limestone, containing no fossils, 

 and supplies the whole district with lime. 



North of the Lukuga the country is almost flat for a distance of 

 10 miles or so and for some way inland. About one mile north of 

 the outlet there is a small stream, the Lubui, flowing into the lake. 



Ten miles from the Lukuga the country rises sharply again at 

 Kahangwa, where I landed to look at the formation which strikes 

 out into the lake in a sharp bluff composed of dark-grey contorted 

 phyllite. At Mtowa the formation seems to be principally schists. 



Again crossing the lake, I found soft grey sandstones which 

 continue north to Ujiji, but in many places here is open plain land 

 and the rock is covered with soil and vegetation. 



Immediately north of Ujiji the country rises again precipitously 

 from the lake shore, showing sandstone formation containing thick 

 beds of conglomerate, dipping generally east about 20°. These 

 sandstone beds rest on granite, which can be seen above the water 

 line at Viuwko and Lumungi. 



North of Lumungi the sandstones give place to granites, gneiss, 

 and schists, which form the main constituents of the mountain 

 range running north along the shore and up past Usambura, where 



