Geological Society. 309 



repose in general also conformably on the red sandstone. The 

 greatest height attained by the formation is the Castle Hill near Pal- 

 mella, the summit of which is 930 feet above the level of the sea, 

 and at this point two lines of disturbance meet. Fossils are very 

 abundant in some of the beds, but sufficient attention has not yet 

 been paid to them to permit their being compared with the organic 

 remains of other tertiary districts. A long-hinged oyster, Ostrea 

 longirostris, Mr. Sharpe considers identical with a species common 

 in the tertiary deposits of the south of S])ain. Small quantities of 

 quicksilver have been found in several places in a bed of sand im- 

 mediately above the blue clay or central division of the formation. 



(c-.) Lower Tertiary Conc/lomerate. — This deposit consists in the 

 upper part of distinctly stratified conglomerates, composed of lime- 

 stone pebbles imbedded in a calcareous matrix ; and in the lower 

 of sands, grits, gravel, and marl. Within the district examined by 

 Mr. Sharpe, it occurs only on the Lisbon side of the Tagus, forming 

 a band from that city by Odivellas, Camarate, Loures, and Tojal, 

 to the neighbourhood of Alhandra, on the banks of the Tagus, and 

 skirting the western and north-western boundary of the Almada 

 beds. The conglomerate occurs also on some of the detached hills 

 between Belem and the Bay of Cascaes. The deposit dips to the 

 south-east under the Almada beds at an angle of 10° or 15°, but in 

 the lowest strata the dip is 30°. For a short distance south of 

 Alhandra, the conglomerate rests upon the red sandstone, but 

 throughout the remainder of its range upon basalt. No organic 

 remains were noticed in the deposit. 



SECONDARY FORMATIONS. 



In few countries can the separation between the tertiary and 

 secondary formations be more strongly marked than in the neigh- 

 bourhood of Lisbon. The deposits of the older class of rocks, Mr, 

 Sharpe states, were disturbed and denuded previously to the com- 

 mencement of the tertiary epoch, and an immense mass of basalt is 

 interposed between the newest of the secondary rocks and the most 

 ancient of the tertiary series. 



(rf.) Hippurite Limestone. — The upper part of this formation con- 

 sists of alternations of marl and limestone, succeeded by beds of 

 limestone containing thin horizontal beds of flint ; and the lov/est 

 part of various strata of compact limestone ; amounting in the whole 

 to a thickness of above 500 feet. The formation is confined to the 

 north of the Tagus, where it presents several distinct bands, which 

 rest upon the red sandstone, and are overlaid by basalt. The most 

 southern tract extends from Cascaes Bay nearly to Loures ; another 

 irregular strip ranges from Montelavar to a little to the eastward of 

 Bucellas ; and a third district, commencing near Villa Franca, 

 stretches to the north beyond the range of Mr. Sharpe's district. A 

 portion of Lisbon also stands upon Hippurite limestone. In some 

 parts, especially on the coast, the dip is slightly towards the 

 south-east, but from Loures to beyond Bellas it varies from 30° 

 to 50° in the same direction. The strata do not always rest con- 

 formably on those of the subsequent red sandstone, for near Cas- 

 caes, the limestone beds are horizontal, and the sandstone on which 



