The breadth of the entroughed bed varies from 700 yards to two miles where it most dispreads itself. The current increases from the normal three to five knots in rare places; the surface loses the glassiness of the lower section, and at once shows the boiling and swirling which will be noticed near the cataracts. The shores are often foul, but the midway is mostly clear, and, where sunken rocks are, they are shown by whirlpools. The flow of the tide, or rather the damming up of the lower waters between Porto da Lenha and the mouth, causes a daily rise, which we found to measure about a foot; thus it assists in forming a treble current, the rapid down-flow in the Thalweg being subtended by a strong backwater on either side carrying a considerable portion in a retrograde direction, and showing a sensible reflux; this will continue as far as the rapids. In the Amazonas the tides are felt a hundred leagues from the mouth; and, whilst the stream moves seawards, the level of the water rises, proving an evident under-current. Mr. Bates has detected the influence of oceanic tides at a point on the Tapajos, 530 miles distant from its mouth, such is the amazing flatness of the country's profile: here we find the reverse. The riverine trough acts as wind-conductor to a strong and even violent sea-breeze; on the lower section it begins as a ground- current--if the "bull" be allowed--a thin horizontal stratum near the water, it gradually curves and slides upwards as it meets the mountain flanks, forming an inverted arch, and extending some 2,000 to 3,000 feet above the summits. At this season it is a late riser, often appearing about 3 P.M., and sometimes its strength is not exhausted before midnight. The brown water, grass-sheeted at the sides, conceals the bright yellow sand of the bed; when placed in a tumbler it looks clear and colourless, and the taste is perfectly sweet--brackishness does not extend far above Porto da Lenha. Yet at Boma the residents prefer a spring near the factories, and attribute dysentery to the use of river-water. According to Mr. George Maxwell, the supply of the lower bed has the quality of rotting cables, and the same peculiarity was attributed to the Tanganyika. Of late years no ship has ventured above Boma, and boats have ascended with some difficulty, owing to the "buffing stream." Yet there is no reason why the waters should not be navigated, as proposed in 1816, by small steamers of good power, and the strong sea-breeze would greatly facilitate the passage. In older and more enterprising days merchant-schooners were run high up the Zaire. The master of a vessel stated to Tuckey that he "had been several voyages up to the distance of 140 miles from the mouth" without finding any difficulty.