limestone appears to be nearly of the same era with the Calcaire Grossier of Paris, and is separated only by a large desert plain from the deposit of shells last mentioned at Bonjem. The probable connexion of these strata with the tertiary formations in other adjacent parts on the coast of the Mediterranean, has been already suggested. 5. Soft, highly calcareous marl stone, of a light mottled gray colour, resembling in appearance the chalk marl of England: it is said occasionally to be streaked with red, and to contain modules of flint. It occurs in the Mountains of Mejdool, in lat. 26. 6. Quartzose sand dispersed through a matrix of indurated green clay, and affording the materials of which the town of Traghan is built. It is probable that these two last specimens, 5 and 6, are. from strata not more ancient than the chalk of England, and possibly connected with the tertiary formations, No. 3 and 4. S EW B E D SAND STONE. 7. Sand collected fifty miles on the north of Sockna, during a gale of wind from the drift sand, which is blown about the desert. I t is composed of extremely minute grains of red semi-transparent quartz; observed with a lens, these grains appear to be rounded fragments, and present no crystalline facets. They possess, in a strong degree, that peculiar tint of red, which has caused the name of red sand stone to be applied to certain extensive formations which it pervades in Europe. The frequent occurrence of salt springs, and of rock salt and gypsum in the deserts of Africa, goes far to identify the sand of this continent with the new red sand in the south of England, which is Characterised by containing similar mineral substances. It is still farther allied to it in being accompanied by strata o f calcareous breccia and beds of limestone; in all of which magnesia is a considerable ingredient. 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° ■&: 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. Elat 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°. IS. Fibrous gypsum passing into foliated, apparently from a matrix of ochreous marl stone. 14. Crystals o f 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. I t is probable these last four specimens come from a stratum
27f 50
To see the actual publication please follow the link above