8, 9, 10. Ferruginous concretions, forming aetites or geodes in the red sand shore. The broken fragments are compact, sonorous, and of a dark liver colour, having a shining polished surface. The sand which formed their matrix still adheres to the exterior of some of them. They occur on a plain and a mountain near Om el a Beed. In lat. 27°⁵⁄₁₀: they are here so abundant, as almost entirely to cover the ground, and impart to it a dark red colour. This accumulation of them probably arises from the wind having drifted away the fine sand, in which they were formed, leaving behind the heavy bodies in question. A little farther north, at the foot of the Pass of Kenair, near some steep sand hills, is a narrow bed almost entirely composed of tubular concretions of iron of similar origin, irregularly ramifying through the sand like roots of trees, and producing a rugged appearance, which at first sight resembles a bed of lava. 11. Flat lamina of variegated sand stone, held together by a calcareous cement, and covered on each side by small spherical tubercles closely studded by the side of each other. Similar concretions are common in the imperfect beds of sand stone strata of all formations. 12. Flesh-coloured marl, full of small irregular crystals of selenite. The colour of this marl resembles that of the rock marl of England: it is from a plain near Gatrone, lat. 25°. 13. Fibrous gypsum passing into foliated, apparently from a matrix of ochreous marl stone. 14. Crystals of calcareous spar imbedded in yellow-ochre. Found with No. 13, in the same mountain with the Calcaire Grossier, No. 4, thirty miles south of Benioleed. 15 and 16. Fibrous and foliated gypsum from a similar matrix of ochreous marl to No. 13 and 14, and found on the same plain, near Bonjem, with the two species of cardium, No. 3. It is probable these last four specimens come from a stratum more nearly allied to the gypsum formation of Paris than to the red marl to which I have referred the other specimen of gypsum, No. 12. MAGNESIAN LIMESTONE, OR DOLOMITE. 17. Limestone, very compact, and strongly impregnated with magnesia, and is of a yellowish white colour; occurs split into small laminated fragments, like broken tiles. The ground is covered with these fragments, which break and rattle under the feet like pottery. It is found in the plain between Zuela and Omesoguin, lat. 26°. 18 and 19. From the plain that lies between the Black Mountains and Pass of Kenair. Both these specimens are compact limestone, of a dark flesh colour, and contain much magnesia. This plain is covered with small shining fragments of this limestone, particularly near El Gaaf; and their exposed surfaces are corroded and furrowed over with the small irregular grooves and channels already mentioned in the note to No. 1. 20. Flesh-coloured dolomite, mottled with yellow. From the north base of the Black Mountains.