If a transverse section were taken about the middle of the cataract region, there would be first an ascent from the river, almost perpendicular, of from 300 to 500 feet in about one-third of a mile, then a much steadier rise of some 500 to 700 feet in two miles, and then a rise of another 500 to 700 feet in eight miles, with a further steady rise for five miles, so that the actual valley in the cataract region might be estimated roughly at from twenty to thirty miles in breadth. The river itself varies from 300 yards to one-and-a-half or two miles wide at mid-flood; while the difference between the highest water of the rainy season and the lowest in the dry season, varies from forty feet in the worst parts to about three feet on the lower river. To the geologist the country between the coast and Stanley Pool is best studied along the river. The first low hills approach near to the mouth of the river, which is about seven miles wide, and devoid of a delta; the next step in the plateau occurs at five miles west of Mboma, fifty miles from the coast, where the tops of the ‘hills’ are from 500 to 700 feet in height. There we find a red clay yielding copal above granitic rocks. The banks grow steeper and the river narrows, until at Vivi the first serious obstacle is met, the plateau level being about 1,700 feet, and the river about 600 yards wide. Just above this is the fierce Yelala Cataract; indeed, nowhere can you properly speak of falls; a drop of fifty feet, which would be a fine scene on an ordinary river, is almost disregarded by the Congo. The bed of a cataract must be of very hard rock, and down this inclined plane, the river, nipped tightly by the hills, rushes with fearful velocity, leaping in mad waves, foaming and raging at its rocky obstacles. In some of the milder cataracts it rushes down a swirling mound of water, which projected into the quieter low level at the foot of the cataract, races on as a heap of waters for nearly half a mile, before it consents to swirl about at the lower level. Fierce up currents run along the shore at such points, which would draw boats or canoes into the swirling current, while along the edges of these counter-currents are great whirlpools, giving way to each other, disappearing, and breaking up into ‘caldrons,’ the whole surface heaving and seething. In a creek three miles below the Ntombo Cataract we have watched this heaving. The water would flow outwards from the creek, then meeting the impulse of a fresh heave, would flow back until it would remain stationary for some twenty seconds, often two feet higher than what it was a minute ago. This flows backwards and forwards in the creek, recurring every two minutes or minute and a half. [Illustration: A LOAD.]