It would seem strange that there should be this surf, not only with a perfect calm, but with a glass-like sea. There was, however, where we lay, a slight heaving of the water; and these heaves, as they bore landwards, became, within a mile of the coast, billows, and then dashed upon it with the extremest fury, as if the Atlantic, in contact with Africa, required not the aid of wind, but shook it with the spontaneous heaves of its majestic breast. We lay for hours with the same marks on--as if we had been a rock. The tide rises and falls upon the shore, but does not run along the land. The Atlantic merely heaves up and down, but shifts not its place. It is met in front by a straight line; and the tidal currents of the coast of Europe are stopped at the great indraught of the Straits of Gibraltar; so that to the southward there extends a region of some hundred miles of dead water. Hence the violence of the action of the waves upon the shore. With our indented and slanting coasts, there is always a current running in front of the land, which serves as a breakwater against the effects of the rise and fall of the tide: here there is no such protection. In like manner may be explained the incessant disturbance of the Bay of Biscay: the horns break the tides along the shore, and the Atlantic surges in upon the congested waters. Below Rabat a current begins to be sensible; it runs south. At Mogadore it reaches the speed of three knots an hour. There are combined to produce it, the sweep of the back eddy of the Atlantic, and the nightly gales which blow from the sea into the interior of Africa to supply the rarification of the Great Desert. This nightly indraught begins only at the province of Sus; to the north the ordinary land and sea winds prevail. In these latitudes it is calm at sun-rise and sun-set. The breeze freshens by night from the land, by day from the sea--the former breathing a gentle gale, the second reaching to a top-gallant breeze. The sand is not blown up from the sea, as some have supposed, nor down from the Desert. In travelling over it, you would suppose that you were crossing a rocky country. On the coast its structure is exposed, and there it appears to be a bank of sand, with a coast of stone. Worn by the waves, the unsupported rock comes tumbling down, and the fragments often sticking on the edge form the breakwater. The “conformably overlying” rock, is an induration of the sand by oxide of iron; sand, newly exposed, immediately begins to crust. This bank must have been left by the waters of the deluge, escaping westward, charged with the sand of the interior. This idea was first suggested to me by the deposits on both sides of the rock of Gibraltar. The sand blocks up to its very roofs a cavern which opens to the eastward.