A short descriptive catalogue of the specimens which have been brought home, with the assistance of the map in which all the names alluded to are inserted, will give the most ready information they are calculated to afford. The specimens are as follow: BASALT. No. 1. Basalt, nearly black, much impregnated throughout with carbonate of lime, and interspersed with small circular cells, that are partly or wholly filled with common or with magnesian carbonate of lime. The decomposition of this rock forms small spherical fragments of considerable hardness, the surface of which, by long exposure, has acquired a kind of polish or glossy aspect, and is irregularly pitted or indented all over with small cavities of various depths, from the destruction of the calcarous matter that originally filled them. A similar appearance of glossy polish is found on all the calcareous specimens from this country, which appear to have been long exposed to the action of the atmosphere. In some of these the surface is entirely smooth and even; in others, it is furrowed over with minute grooves and channels, intersecting each other with irregular curvatures, and resembling the appearance produced on the surface of compact limestone that has been submitted to the action of acids, or corroded by small marine worms. It is not easy to determine the cause of this irregular destruction of the surface of limestone, whose substance appears to be entirely uniform: it is probably the same that gives it the glossy polish; but it seems doubtful, whether the agent producing it be the continual drifting of fine siliceous sand, or the action of the atmosphere under exposure to a burning sun. A similar gloss appears on the surface of many fragments of flint and compact siliceous limestone that have been long exposed on the surface of the soil, on the summit of Martre near Paris; and in this case, I think, it can only be referred to the action of the sun and atmosphere. The chain of the Soudah or Black Mountains appears to be composed of this basalt; they rise to an elevation of about 1500 feet, being situated at a short distance on the south from Sockna, and extending about 100 miles in breadth from north to south, and in length as far as the eye can reach, from east to west; they are perfectly barren, of irregular form, occasionally broken into detached masses, and sometimes rising into cones. Their elevated plains are in some parts covered with the small spherical shining fragments above described. The latitude of this chain is from 28·40. to 27·30. north. Traces of basalt occur also near Tripoli, in lat. 32. at a spot called Black Dog, on the north of Beneabbas, and in a valley through which the road passes from Beneabbas to Benioleed.