INTERESTING PHENOMENON 913 



subject of the Lukuga, and are better able than myself to deal with it. I can- 

 not satisfactorily account for the existence of this interesting phenomenon 

 otherwise than by supposing the formation of the extraordinary deep depres- 

 sion in the bosom of the broad plateau filled by the waters of the Tanganyika 

 to be post-diluvain. If the ideas of one accustomed to read geological history, 

 and to speculate on past ages from existing traces in the hard rock or moun- 

 tain contour, may be permitted to see the light, I would say that subsequent 

 to the retreat of the ocean to its present bed, the Malagarazi and the Luwegeri 

 rivers have flowed over this present enormous gulf, and channelled their way 

 for their exit westward, first severing the Kiyanja from the Kilunga ridge. 

 This great depression was in these days an apparently firm plateau with the 

 same rolling surface as Unyamwezi and Uhha now present ; and the two rivers, 

 joined by others of less magnitude, flowed on undisturbedly to the Lualaba 

 for centuries, perhaps ages. For in what other manner could this deep break 

 in what must evidently have been long ago one firm, unbroken, compact ridge, 

 have become so smoothly worn down, a thousand feet and more, so low as to per- 

 mit the gently flowing Luindi to sweep by its base from the east. It required 

 a mightier volume of water than the Luindi, with no other source of supply 

 than the ooze of the Mitwansi, three miles east of Kiyanja, and until the 

 present year such supply must have been scanty in the extreme. 



"If it be granted that such was, or might have been, the condition of 

 this region at that time, the subsequent changes which took place are easy 

 enough to arrive at. We may imagine volcanic agency, then, as heaving up 

 this plateau, rending the solid earth, and heaping along the edges of the deep 

 chasm it created long lines of mountain ranges, so changing its former smooth 

 rolling surface into its present rugged and uneven aspect. The great stream 

 which formerly drained all this section and rolled between the Kihinga and 

 Kiyanja ridges, having its ancient bed disrupted, fell abruptly into the im- 

 mense gulf in several and separate courses, till a stream of short length and 

 little volume is created, flowing from the eastern slopes of the above-named 

 ridges south-eastward, to be in due time known as the Lukuga ; since which tre- 

 mendous wrack of nature half of the waters with inverted courses have as- 

 sisted the other half to fill up the chasm, appearing to be now on the eve of 

 fulfilling their task. 



"The visible effects of this great geological change are not the same at 



the southern end as they are further north, and about the centre. At the 



southern end, the plateau, with its folds upon folds and layers upon layers 



of firm rock, drops abruptly down to the blue-green depths of the lake, and 



voyagers coasting along those shores appear to be gazing at the zenith, 



as they look up at the few shrubs and trees growing upon the edge of the 



tawny plateau. But at the centre, especially about Tongive on the east side 



and Tembive on the west side, we appear to be in the vicinity of the origin 

 q4 



