_(f) The Ndriti Basin or Gap._—This great hollow in the side of Seatura, which I have named after the town in its midst, is apparently a crateral cavity now drained by the Ndama river, and its tributaries, and covered with dense forest to such a degree that a general view of the whole is impracticable. The glimpses, however, that one obtains of the mountain scenery are very grand, the town 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;[36] whilst its mountainous 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[37]; 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.