68 A NATURALIST IN THE PACIFIC chap. 



of Ndriti lying in the midst of mountains that rise almost on all 

 sides of it except on the west. This great cavity is contracted at 

 its mouth a little below the town and expands in its interior, where 

 it must be two or three miles in width. Its floor is fairly level and 

 is elevated only about 200 feet above the sea ; x whilst its mountain- 

 ous sides rise to 2,000 feet and over. 



As shown in the map there are two breaks in the outline of this 

 ancient crater, the one on the west through which the Ndama 

 river flows, the other on the south where the dividing ridge, 

 separating it from the Nandi Valley is under 700 feet in elevation. 

 The Nandi Gorge, as I will term the last-named, is a narrow 

 picturesque ravine leading through the mountains from Nandi 

 to Ndriti. One follows up a rocky stream-course hemmed 

 in by precipitous sides until the top of the gorge is reached, 

 when the watershed is crossed, and the descent is then made 

 to Ndriti by one of the tributary stream-courses of the Ndama 

 river. 



Two or three large rapid streams, after draining its mountainous 

 slopes, unite within the basin to form the Ndama river, which, as it 

 issues from its mouth, becomes a comparatively placid stream 

 rolling sluggishly along to the sea, some five or six miles away, 

 with an average drop of about thirty feet in a mile. In the course 

 of ages the original configuration of this great hollow has doubtless 

 been extensively modified by the denuding agencies. The rainfall 

 on the mountain-slopes must be very great, probably not under 

 250 inches in the year 2 ; and Ndriti, though only 200 feet above 

 the sea, is in all probability on account of its situation one of the 

 wettest places in the island. The rivers have evidently been 

 important factors in reshaping the original cavity. 



Nearly all the rocks exposed in situ in the beds of the rivers 

 and streams in the floor of the great Ndriti basin, and for 300 or 

 400 feet up its sides are more or less highly altered basic rocks, to 

 which the old and the new names of greenstone and propylite may 

 be fitly applied. They often sparkle with pyrites, and not un- 

 commonly effervesce with an acid, so that one is apt to imagine 



1 In one of my traverses I crossed a level district extending a mile N.E. of 

 Ndriti without changing my elevation. 



2 At Delanasau, on the north or dry coast of the island, the average rainfall, 

 according to many years' observations by Mr. Holmes, is about 1 1 5 inches. At 

 Wainunu, near the wet or south coast, the observations of Mr. Barratt and others 

 extending over 16 years give an average of 160 inches. In the mountains this 

 would be nearly doubled. 



