88 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Jan. 10, 



represented in fig. 2, amongst which Mr. Etheridge has deter- 

 mined Exogyra conica, Ostrea Leymerii, and 0. Boussingaulti. He 

 considers the beds to be of Neocomian age. The hard band C is 

 almost entirely made up of Exogyra conica. 



Two or three miles south of Saff'e another section occurs, known 

 as the " Jew's Cliff; " and from this Dr. Hooker, who landed on his 

 homcAvard voyage, obtained a few fossils, viz. : — several unde- 

 terminable species of Pecten ; an Ostrea allied to 0. Virleti ; and 

 a scutelliform Echinus of an unknown type, which Mr. Etheridge 

 proposes to place under a new genus, and names Rotuloiclea jim- 

 hriata^. All these Mr. Etheridge supposes to be of Miocene age; and 

 the "Jew's Cliff" section may probably give the key to the age of 

 the beds of the Morocco plain in which we found no fossils. 



I am indebted to Mr. Carstensen, H.B.M. Viceconsul at Mogador, 

 for a specimen of Ostrea Leymerii, brought to him by a Moor from 

 Agader, and obtained, at a height of 1500 feet, on the flanks of the 

 maritime termination of the Great Atlas range, 160 miles south of 

 the Saffe section. 



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, pre- 

 senting a weird expanse of sea-like waves of sand, on a scale vastly 

 greater than any thing 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 

 vaUey-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 viole^t westerly gales blowing the sand vp the angle of repose, 

 and accumulating it in fountain-Hke showers over the rounded backs 

 of the sand-hill ranges. 



It is worthy of note that the subaerial ripple-markings superim- 

 posed 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 Morocco. — We now turn inland ; and before refer- 

 ring 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, 

 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 mUes inland, the average level of the plain, about 

 1700 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 (PI. III. figs. 3 & 4), 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 hiU were the fundamental beds visible, and seen 

 * See Appendix, p. 97. 



