X NDREKE-NI-WAI VALLEY 151 



valley, above the village of Mbale-mbale, is broad and low-lying ; 

 and one can ascend it to the vicinity of Waisali, three to four miles 

 from the river's mouth, without attaining an elevation of 100 feet 

 above the sea. The main stream, which flows down from Waisali, 

 is joined near Mbale-mbale by a more impetuous stream that 

 descends the steep mountain-sides just to the east of the Koro- 

 tini Bluff. 



The valley of the Vatu-kawa River is bounded by lofty moun- 

 tain-ranges that rise to elevations varying from 2,000 to 3,500 feet. 

 On the south side lies the Mariko Range, on the east lies Mount 

 Mbatini, the most elevated peak of the island, whilst on the north 

 rise up the steep slopes of the Koro-tini Range and of the moun- 

 tainous " divide." The valley has such a gentle gradient that one 

 can follow it inland for five or six miles from the estuary to the 

 vicinity of Nukumbolo without exceeding an elevation of 100 feet 

 above the sea. Below Na Salia the valley is confined between the 

 hills that approach the river; but above that village it is very 

 broad ; and on account of its slight fall the river here often 

 changes its course, so that the floor of the valley is strewn with 

 water-worn blocks and pebbles marking the old channels. 



The Vatu-kawa River, which rises on the west slopes of 

 Mbatini, flows with a placid current past Nukumbolo and Na 

 Salia, until it reaches the village of Vatu-kawa, where it is joined 

 by its impetuous tributary, the Wai-ni-ngio, "the river of the 

 shark." This affluent, after descending the steep slopes of the 

 Koro-tini mountains, bursts through the dividing range that 

 separates the Mbale-mbale and the Vatu-kawa valleys. It would 

 seem that the Wai-ni-ngio without any great effort on its part 

 might become a tributary of the Mbale-mbale River. 



The great character of these two valleys, as shown above, is 

 their little elevation above the sea. For miles inland the level 

 does not attain 100 feet, and high ranges rise steeply in each case 

 on either side to 2,000 feet and over. Here, as in the instance of 

 most of the large valleys of the island, the original configuration 

 of the surface was not dependent on river-erosion. Rivers no 

 doubt have done much to carve out the lesser and to deepen and 

 widen the greater valleys ; but, as is often remarked in this work, 

 the main features of the surface were in existence before the 

 emergence of the island from the sea. 



The geological formation of the slopes of these two valleys is 

 described in the accounts of the various ascents of the mountains 

 bounding them. Since foraminiferous tuffs occur high up their 



