supposed by M. Nyst to be Miocene, the upper part of the escarpment resembling the beds of later age before described.

An examination of the higher points of the western coast near Saffi, and at Azfi in the province of Abda, near Mazagan, tended to establish the fact of the occurrence of Pliocene beds in the district.

At Cape Saffi, 180 metres in altitude, a reddish calcareous sand was met with abounding in Cyclostoma, Cylindrellas, and a species of Helix differing from that at Mazagan; and at other points, including the hill of Aher and at Sidi Bousid, white marls and sands associated with calcareous sandstones were met with analogous to the supposed quaternary beds in the neighbourhood of Mazagan.

The only other point in the geology of the coast-line I have to refer to is the great mass of blown sand surrounding Mogador, presenting a weird expanse of sea-like waves of sand, on a scale vastly greater than anything of the kind on our own coast, mimetic of mountain-chains and bold escarpments in miniature, differing only from true hill-and-valley structure in the absence of continuous valley-lines, the hollows being completely surrounded by higher ground. Many of the ranges of sand are from 80 to 100 feet in height, and their perfectly straight scarped faces are produced by the violent westerly gales blowing the sand up the angle of repose, and accumulating it in fountain-like showers over the rounded backs of the sand-hill ranges.

It is worthy of note that the sub-aërial ripple-markings superimposed on the greater undulations, occupy a reversed position with reference to the prevalent winds, their long side facing the wind, with the more vertical straight scarps on the lee side. The moving sand in this case is drifted up the long side, and falls over the scarp at the angle of repose.

The Plain of Marocco.—We now turn inland; and before referring to the details of the structure of the Great Atlas range, it will save repetition if I briefly describe the general contour of the district under consideration. Leaving the sand-hills, which die out inland, and travelling westward, we gradually ascend over an undulating country, in aspect somewhat like the Weald of Sussex, covered for 30 miles with Argan Forest, till we reach, at 60 miles inland, the average level of the plain, about 1,700 feet above the sea.

The fundamental rock is here rarely to be seen; for the entire face of the country is shrouded over by a sheet-like covering of tufaceous crust (fig. 3), rising over hill and valley, and following all the undulations of the ground. Only in river-beds and here and there by the side of a hill were the fundamental beds visible, and seen to consist of alternations of hard and soft cream-coloured calcareous strata, dipping and undulating in various directions at low angles, and so closely resembling the surface crust that it was difficult to distinguish the one from the other, unless the surface crust happened to lap unconformably over the scarped exposures of the stratified beds. This singular deposit varies in thickness from a few inches to two or three feet, and is taken advantage of by the Moors for the excavation of cellars in the soft ground, over which the crust forms a strong roof. These are termed matamoras, and are used for the storage of grain, and as receptacles for burying the refuse from the villages. The calcareous crust in the neighbourhood of Marocco is extensively burned for lime. In section it presents a banded agatescent structure, often much brecciated. It is impossible it can have been deposited by any waterflow, as completely isolated hills are shrouded over by it as thickly as the valley bottoms; and the only satisfactory explanation of its origin I can suggest is, that it results from the intense heat of the sun rapidly drawing up water charged with soluble carbonate of lime from the calcareous strata, and drying it layer by layer on the surface, till an accumulation several feet thick has been produced. The rapid alternations of heavy rains and scorching heat which take place in the Marocco plain are conditions favourable to this phenomenon, which is unknown in northern temperate climates.

Fig. 3.