112 Mr. D. Sharpe on the Geology of 



this memoir, the north bank of the Tagus being formed of older rocks ; but it 

 occurs again near Cartaxo, Santarem, Thomar and Abrantes, the last town being 

 its extreme limit to the eastward. I do not know if it exists along the eastern 

 edge of the basin, but to the south it forms the hill of Alcacer do Sal, where it 

 rests upon slate clay, the intermediate secondary formations being absent. 



In the centre of this tertiary district, a ridge of older rocks extends from Pal- 

 mella to Cape Espichel, skirted by a zone of the Almada beds from St. Ubes to 

 Palmella (Sect. 9, 11 and 13), and thence westward through Azeitao nearly to the 

 coast, where they are concealed by the upper tertiary sand, overlying both these 

 and the older rocks. Throughout this circuit the Almada beds rest upon red sand- 

 stone, and are more elevated than in the locahties before described, the dip 

 being usually from the subjacent formation: thus between St. Ubes and Palmella 

 their inclination is about 30° S.E., and from Palmella to Azeitao between 25° and 

 30° N.E., being rather greater in the lower than in the upper beds ; but at Pal- 

 mella, where the two lines of elevation meet, the disturbance has been more con- 

 siderable, and the dip at the Castle-hill varies from 15° to 50° N. It is probably 

 from the same cause that the formation attains its greatest height at this point, the 

 castle being 930 feet above the sea (PI. XV. Section 9). 



A detached mass of the formation also occurs at the western end of the Serra 

 de San Luiz, between St. Ubes and Azeitao, abutting unconformably against the 

 edges of the elevated beds of red sandstone, which form that steep hill ; its dip, 

 about 30° N., agrees with that of the same beds in the neighbouring Serra de 

 Azeitao (Plate XV. Section 1), so that the valley between mast have been occu- 

 pied originally by the tertiary beds. 



The most violent dislocation of this formation is on the bank of the Sado, at the 

 foot of the Serra de Vizo (Plate XV. Section 13), where an outlying mass of the 

 limestone dips at 80° toward the older red conglomerate, having been elevated 

 beyond the perpendicular. 



I did not observe the blue clay in this neighbourhood, nor could I examine the 

 beds enough to ascertain to which part of the formation they belong ; they are 

 mostly coarse, rotten, sandy limestones, containing many casts of shells, and pro- 

 bably belong to the lower division of the formation. 



This deposit affords the best land in the neighbourhood, both for corn and vines; 

 and it is peculiarly suited to the growth of the olive, which thrives to greatest 

 advantage in a light and semi-calcareous soil. 



Mr. George Sowerby has examined my fossils, and also an excellent collection 

 made near Lisbon by James Smith, Esq., of Jordan Hill, who has very kindly 

 allowed me the fullest use of the information derived from it ; among them Mr. 

 Sowerby has found the following shells, besides about twenty undescribed species. 



