the Neighbourhood of Lisbon. \ \ \ 



Quicksilver has been found in several places in the sand immediately above the blue clay, but in very 

 insignificant quantities. 



Not having examined this formation in equal detail elsewhere, I can give but a 

 general sketch of its position. On the southern side of theTagus, it forms the cliffs 

 from Trafaria to Casilhas, the dip of the strata being from 10° to 15° S.E. There 

 are three considerable faults in these cliffs. At Casilhas the beds to the west of 

 the village are raised about 100 feet above their prolongation on the other side of 

 the street ; at Fonte de Pipa, on the contrary, those on the west of the fault are 

 about 130 feet below the same beds to the eastward ; and at San Lourenco a simi- 

 lar dislocation has taken place to the extent of about eighty feet. Owing to these 

 faults, a more extensive section of the formation is obtained than the cliffs, which 

 are only 280 feet high, would otherwise afford. 



North of the Tagus the Almada beds begin on the coast, a little to the west of 

 Fort St. Julian, resting on the secondary limestone, and they reach as far as the 

 Oeiras River, where they are cut off by a fault, — one bank of the river consisting of 

 these beds, and the other of the secondary limestone ; both rocks being also hori- 

 zontal and at the same level. 



For about ten miles to the eastward, the upper beds appear to have been de- 

 nuded ; and the tertiary strata are seen only at the tops of some hills about Santa 

 Catarina and San Joze de Riba-mar. These outliers consist of the lower tertiary 

 conglomerate, occasionally covered by small patches of the Almada beds. (See 

 Plate XV. Sections 1 and 3.) 



The Almada beds reappear in the middle of Lisbon, and continue along the 

 north bank of the Tagus to the little village of Verdelha. At their western edge, 

 under Lisbon, the upper beds rest unconformably upon the secondary limestone 

 (Plate XV. Section 3), the Rua de San Bento marking very nearly the line of 

 union of the two formations. To the north-west, the Almada series is bounded by 

 the valleys of Odivellas and Vialonga, and rests conformably upon the lower ter- 

 tiary conglomerate. Throughout this district, the dip of the Almada beds is from 

 5° to 10° S.E. The lower streets of Lisbon stand upon the blue clay, which may 

 be traced for some miles up the Tagus between high- and low-water levels, all 

 the cliffs toward the river consisting of the deposits above that stratum. The 

 lower beds may be seen cropping out on the land-side of the deposit, but there is 

 no good section of them there. 



The Almada beds in this part agree so nearly in dip and strike with those on 

 the south bank of the Tagus, and with the detached outliers between Lisbon and 

 the sea, as to prove that they were once continuous, and have been separated by 

 denudation. 



Beyond Verdelha the formation is not visible within the district described in 



