122 Mr. D. Sharps on the Geology of 



4. Slate-clay and Shale with trap. (PI. XIV. and PI. XV. Sect. 1, 2, 4, 5 and 7.) 



In the neighbourhood of Cintra, the Espichel limestone rests conformably upon 

 an argillaceous formation, which constitutes a low rounded ridge, encircling the 

 Cintra hills, which may be most advantageously examined at Ramalhao and 

 Linho. 



The upper beds consist of shale and schist varying much in character ; below 

 them are numerous beds of slate-clay alternating with a variety of igneous rocks, 

 and the lowest part is a thick deposit of dark shale. In no portion did I find any 

 organic remains. 



The beds of igneous rocks vary from five to twenty feet in thickness, and the 

 shale-beds are still thicker. The whole are regularly interstratified without any 

 signs of disturbance. The shale rests with perfect conformity upon the San Pedro 

 limestone, and dips on all sides from the axis of the Cintra chain at angles varying 

 from 30° to 60°. 



Near Ramalhao, where the series is most developed, there are twenty or thirty 

 distinct alternations of igneous rocks. On the north side of Cintra the formation 

 is less important, and becomes gradually thinner; and in the cliffs at the Praia de 

 Adraga it does not exceed 200 feet in thickness, and contains only one igneous bed, 

 about twenty feet thick. I did not follow the formation quite round the south of 

 Cape Rock, and do not therefore know its exact importance at that point. 



It is difficult to account for these alternations of igneous and aqueous beds, ex- 

 cept by supposing that the igneous matter was poured out at intervals during the 

 accumulation of the shale. There is no evidence to prove, whether these eruptions 

 took place from the spot, where the granite hills of Cintra were afterwards elevated. 

 The original formation was probably shale, which was altered into slate-clay by 

 the heat of the igneous matter. 



The trappean rocks vary much in character within a few yards in the same beds ; 

 some portions being basaltic, others sienitic. 



5. San Pedro Limestone. (PI. XIV. and PI. XV. Sect. 1, 2, 4, 5 and 7.) 



Below the last formation occurs a considerable deposit of limestone, which rests 

 upon the granite, and forms an inner zone around the Cintra hills. 



The limestone in the upper beds is dark grey or black, and of an earthy struc- 

 ture, and in some places it is very bituminous, and passes into swinestone ; but as 

 it approaches the granite, it gradually changes into a crystalline marble, and from 

 that into calcareous spar. The formation is well exposed on the road-side, and in 



