On the Geology of Gibraltar.

Abstract

The continent of Europe is terminated on the south and that of Africa on the north by a secondary formation of considerable extent, which is cut into two by the Straits of Gibraltar. The prevailing rock on both sides is siliceous sandstone, generally of a yellowish brown colour, which is associated with limestone and shale in different states of induration, and also with subordinate beds of chert and coal. Judging from external character I should pronounce it to belong to the true coal-measures, but the indications furnished by organic remains point rather to the Jurassic group. The evidence however is by no means conclusive; fossils are of such rare occurrence and in such an imperfect state, that no certain inference can, in the present state of our knowledge of its organic remains, be drawn from them. The Gibraltar limestone contains casts of marine shells, chiefly Terebratulæ, one of which appears to be the T. fimbria and the other the T. concinna of the ‘Mineral Conchology,’ both belonging to the lower oolite. A coal-pit has lately been opened about four miles to the north of Gibraltar, but hitherto with no other success than the discovery of a bed of arenaceous shale, with thin flakes of highly crystalline coal. The late Mr. Drummond Hay, the British consul at Tangier, informed me that there are also indications of coal on the African side of the Straits. The hills round the Bay of Gibraltar rise to an elevation of between 200 and 3000 feet,