395 



bourhood of Lisbon and Oporto," by Daniel Sharpe, Esq. F.G.S. & 

 F.L.S. 



Lisbon is shown, by the author of this memoir, to stand upon a 

 range of hills divided by a narrow valley or ravine. The eastern di- 

 vision of the range is stated to be composed of tertiary deposits, and 

 the western of a limestone containing Belemnites. 



The superior bed of the tertiary formations consists of sand in 

 which no fossils were observed, and is about 150 feet thick. It does 

 not occur in Lisbon, but appears on the south side of the Tagus, 

 forming part of its bank and the summit of the neighbouring hills. 



To this bed succeeds a series of strata from 200 to 300 feet thick, 

 and composed of alternations of sand and rubbly, arenaceous lime- 

 stone, containing in great abundance shells of the genera Ostrea, 

 Pecten, Venus, Fistularia, Turritella, Cerithium, Balanus and Ser- 

 pula. The limestone appears on both sides of the Tagus, and though 

 of a perishable nature, is employed as a building material. 



The lowest visible portion of the tertiary series is a bed of blue 

 clay, which also incloses many organic remains. 



The belemnitic limestone is a finely-grained hard rock, occasionally 

 used as a marble, and contains, though rarely, layers of black flints 

 similar to those which are found in the Portland oolite. This lime- 

 stone forms extensive tracts in the neighbourhood of Lisbon, and 

 constitutes a part of the abrupt escarpments along which the far- 

 famed lines of Forres Vedras were constructed. 



The next formation, in a descending order, is a deposit of sand 

 and sandstone, in which no organic remains were noticed. It appears 

 to the north and east of Lisbon, and at Villa Franca, where it under- 

 lies the belemnitic limestone. The celebrated springs of Caldas burst 

 forth in this formation. 



Beneath the sandstone last mentioned, the author observed at 

 Villa Nova da Reinha, to the north of Lisbon, another bed of lime- 

 stone j but he gives no details respecting its nature. 



The next formation described in the memoir is an extensive deposit 

 of basalt, which is stated to occur in contact both with the tertiary 

 series and the belemnitic limestone, but to have produced no change 

 on these strata at its junction with them. 



The granite of the hill of Cintra is said to be composed principally 

 of quartz and felspar with a small proportion of mica and hornblende, 

 and to be divided into large blocks by natural lines of cleavage. On 

 the north side of the hill a limestone is stated to rest against the 

 granite, and on the east a deposit of shale, and the strata of these 

 formations to be highly inclined. 



The author next proceeds to describe the structure of the neigh- 

 bourhood of Oporto. The city stands upon a low ridge of granite, 

 cut through by a defile in which the Douro flows. The granite, 

 composed of quartz, felspar, mica, and hornblende, in the immediate 

 vicinity of Oporto is hard, but at a short distance from it, is decom- 

 posed even to a considerable depth beneath the surface. 



To this formation succeeds a granitic gneiss, the strata of which 

 dip at a considerable angle from the granite, and extends on the west 



