lay just beneath the surface.  We might have got deeper water in the middle, but the boatmen always keep near the banks, on account of danger from the hippopotami.  But, though we might have had deeper water farther out, I believe that no part of the rapids is very deep.  The river is spread out more than a mile, and the water flows rapidly over the rocky bottom.  The portions only three hundred yards wide are very deep, and contain large volumes of flowing water in narrow compass, which, when spread over the much larger surface at the rapids, must be shallow.  Still, remembering that this was the end of the dry season, when such rivers as the Orange do not even contain a fifth part of the water of the Chobe, the difference between the rivers of the north and south must be sufficiently obvious.

The rapids are caused by rocks of dark brown trap, or of hardened sandstone, stretching across the stream.  In some places they form miles of flat rocky bottom, with islets covered with trees.  At the cataracts noted in the map, the fall is from four to six feet, and, in guiding up the canoe, the stem goes under the water, and takes in a quantity before it can attain the higher level.  We lost many of our biscuits in the ascent through this.

These rocks are covered with a small, hard aquatic plant, which, when the surface is exposed, becomes dry and crisp, crackling under the foot as if it contained much stony matter in its tissue.  It probably assists in disintegrating the rocks; for, in parts so high as not to be much exposed to the action of the water or the influence of the plant, the rocks are covered with a thin black glaze.

In passing along under the overhanging trees of the banks, we often saw the pretty turtle-doves sitting peacefully on their nests above the roaring torrent.  An ibis* had perched her home on the end of a stump.  Her loud, harsh scream of “Wa-wa-wa”, and the piping of the fish-hawk, are sounds which can never be forgotten by any one who has sailed on the rivers north of 20 Deg. south.  If we step on shore, the ’Charadrius caruncula’, a species of plover, a most plaguy sort of “public-spirited individual”, follows you, flying overhead, and is most persevering in its attempts to give fair warning to all the animals within hearing to flee from the approaching danger.  The alarm-note, “tinc-tinc-tinc”, of another variety of the same family (’Pluvianus armatus’ of Burchell) has so much of a metallic ring, that this bird is called “setula-tsipi”, or hammering-iron.  It is furnished with a sharp spur on its shoulder, much like that on the heel of a cock, but scarcely half an inch in length.  Conscious of power, it may be seen chasing the white-necked raven with great fury, and making even that comparatively large bird call out from fear.  It is this bird which is famed for its friendship with the crocodile of the Nile by the name ‘siksak’, and which Mr. St. John actually saw performing the part of toothpicker