The altitude of the brim in some parts is considerable; in others, as at Tette and the bottom of Murchison's Cataracts, it is so small that it could be ascertained only by eliminating the daily variations of the barometer, by simultaneous observations on the Coast, and at points some two or three hundred miles inland.

So long as African rivers remain in what we may call the brim, they present no obstructions; but no sooner do they emerge from the higher lands than their utility is impaired by cataracts.

The low lying belt is very irregular.

At times sloping up in the manner of the rim of an inverted dinner-plate--while in other cases, a high ridge rises near the sea, to be succeeded by a lower district inland before we reach the central plateau.

The breadth of the low lands is sometimes as much as three hundred miles, and that breadth determines the limits of navigation from the seaward.
We made three long marches beyond Muazi's in a north-westerly direction; the people were civil enough, but refused to sell us any food.