THE GEOLOGY 0.F GIBRALTAR. 513 



at the surface. Great leading faults are apt to be parallel, and the 

 inferred fault is parallel to the Great Main Fault. 



At Campo there is a good exposure of arenaceous clay or argilla- 

 ceous sand, charged abundantly with molluscan shells (one of which 

 is Terebratula grandis). Echini, and other organisms. The deposit is 

 probably of Pliocene age. Mr. Smith makes some reference to the 

 occurrence of rubbly sandstone beds immediately to the north of 

 the Sandy Plain, in which he found abundant marine Tertiary 

 fossils, referred by him to the Miocene. The particular place he 

 alludes to we did not see ; but there is no doubt that the deposits 

 at Campo rest quite unconformably upon the sandstones of the Queen 

 of Spain's Chair and that neighbourhood. 



Of the more recent deposits to be met with round the shores of 

 the Bay of Gibraltar it is not necessary to speak. There are wide 

 spreads of modern alluvium in the valleys of the Guadaranque and 

 Palmones rivers ; and at higher levels occur older alluvial terraces. 

 It may be worth noting also that at the cemetery near Almirante 

 Tower, red loess, apparently of some considerable thickness, covers 

 all the low grounds that rise from the coast towards the foot of the 

 hills. 



Here it may not be out of place to mention what we saw of the 

 rocks on the opposite coast of Africa. 



By the kindness of the naval authorities at Gibraltar we crossed 

 to Ceuta in the gunboat commanded by the Hon. Algernon Littleton, 

 being accompanied by several members of the Sanitary Commission. 

 About 4 miles from the town we came upon blue slaty rocks, not 

 unlike the Lower Silurian strata of Wales ; and apparently inter- 

 stratified with these were beds of hard grit and many veins of 

 quartz, one of which is a lead-lode now being worked. Though 

 very much contorted, these strata apparently dipped westerly under 

 the strata associated with the mass of Abyla, called by the English 

 Ape's Hill. This mountain has a height of 2308 feet, and forms 

 the African Pillar of Hercules, as opposed to that of Gibraltar. 

 Coasting along the shore, it was easy to see that Abyla consists of 

 limestoue similar to that of Gibraltar, and quite as much disturbed. 

 The strata of both the Pillars strike towards each other, and the 

 shales and sandstones both below and above the limestone appa- 

 rently closely resembled those of the Spanish hills of the Queen of 

 Spain's Chair and the contorted shales and grits that surround the 

 Bay of Gibraltar and form the hills behind Algeciras. Such-like 

 strata apparently form the coast-cliffs as far as the neighbourhood of 

 Tangier, and from thence 12 miles further to Cape Spartel, which 

 latter distance we rode. Immediately west of Tangier the strata 

 consist of shales, which dip under sandstones forming rounded 

 undulating hills of about 800 feet in height. The strata dip in 

 various directions, southerly, westerly, &c. ; and at Cape Spartel the 

 sea-cliffs are formed of white sandstone, with ferruginous springs, 

 like some of our Coal-measure strata. We presume, however, that, 

 like the Abyla, Gibraltar, a nd Algeciras strata, they are probably all 

 of Jurassic age. From the tops of the hills to the east of Tangier 



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