140 THE LAKE REGIONS OF CENTRAL AFRICA. 



with the waters of its rival the Nyanza : it appears 

 moreover, to corrode metal and leather with exceptional 

 power. The colour of the pure and transparent mass 

 has apparently two normal varieties : a dull sea-green — 

 never, however, verdigris-coloured, as in the shoals of 

 the Zanzibar seas, where the reflected blue of the atmo- 

 sphere blends with the yellow of the sandy bottom ; the 

 other, a clear, soft blue — by day rarely deep and dark, 

 like the ultramarine of the Mediterranean, but resembling 

 the light and milky tints of tropical seas. Under a strong 

 wind the waves soon rise in yeasty lines, foaming up 

 from a turbid greenish surface, and the aspect becomes 

 menacing in the extreme. 



It was found impracticable to take soundings of the 

 Tanganyika : the Arabs, however, agreed in asserting 

 that with lines of several fathoms they found bottom 

 only near the shores. The shingly sole shelves rapidly, 

 without steps or overfalls, into blue water. Judging 

 from the eye, the bottom is sandy and profusely strewn 

 with worn pebbles. Reefs and washes were observed 

 near the shores ; it is impossible to form an idea of their 

 position or extent, as the crews confine themselves to a 

 few well-known lines, from which they cannot be per- 

 suaded to diverge. No shoals or shallows were seen 

 at a distance from the coasts, and though islets are not 

 unfrequent upon the margin, only one was observed or 

 heard of near the centre. 



The affluents of this lake are neither sufficiently 

 numerous nor considerable to alter by sedimentary de- 

 posit the depth or the shape of the bed. The borders 

 are generally low : a thick fringe of rush and reed, ob- 

 viating erosion by the element, conceals the watery 

 margin. Where the currents beat, they cut out a short 

 and narrow strip of quartzose sand, profusely strewn 



