.<)08 Geological Society. 



tertiary district, south of the Tagus, included within the author's sur- 

 vey. The strata are usually quite horizontal, except at the edges of 

 the basin, where they rest upon the inclined beds of the subjacent 

 deposits ; and the author did not observe any instance of their 

 having been disturbed. They generally repose upon the Almada 

 limestone, but near Aldea do Meco, to the north of Cape Espichel, 

 they are in contact with the red sandstone formation. No traces of 

 organic remains have been noticed in any part of these sands. In 

 the lower beds a mine of quicksilver was worked profitably during 

 the last century near Coina, south of tiie Tagus ; and the gold dust 

 for which the sands of that river have been so long celebrated, Mr. 

 Sharpe believes, is derived also from the lower or ferruginous sands. 

 (b.) Almada Beds. — A complete section of this deposit is not ex- 

 hibited in the neighbourhood of Lisbon, and the strata are so very 

 irregular both in thickness and composition, that it is difficult to 

 connect the sections displayed at different localities. The strata are 

 best exposed in the cliff south of the Tagus, between Trafaria and 

 Almada. The M'hole of the series is arranged by Mr. Sharpe in 

 three groups, the uppermost consisting of limestone and sands, the 

 middle of blue clay, and the lowest of another series of hmestones 

 and sands : but Mr. Sliarpe does not attach much value to the sub- 

 division ; as the same fossils are found in the beds above and below 

 the blue clay. The deposit constitutes a triangular tract on the 

 Lisbon side of the Tagus, extending from that city to Verdelha, a di- 

 stance of about fourteen miles ; it also caps some hills between Belem 

 and Fort St. Julian. South of the Tagus, it forms the cliffs already 

 mentioned; and a band which ranges from St. Ubes northwards to 

 Palmella, and thence south-west to within a mile of Aldea do Meco, 

 skirting the flanks of a ridge of secondary formations. A detached 

 mass of the Almada beds occurs at the western end of the Serra de 

 San Luiz, between St. Ubes and Azeitao, abutting unconformably 

 against the elevated edges of the beds of red sandstone, and another is 

 on the shore at the foot of San Felippa near St. Ubes. North of the 

 Tagus, the beds incline from 5° to 10° to the south-east; but to the 

 south of the river between St. Ubes and Aldea do Meco, the dip varies 

 from 25° to 30°, and conforms to the position of the band with respect 

 to the ridge of secondary rocks, being to the south-east between St. 

 Ubes and Palmella, and to the north-west between the latter town and 

 A zeitao . The beds of the detached mass near the western end of the Serra 

 de San Luiz, dip about 30° north, and those of the mass on the siiore 

 at the foot of San Felippa, 80° towards the older red conglomerate, 

 having been thrown over beyond the perpendicular. On the coast 

 at Casilhas near Almada, the level of the strata is affected very con- 

 siderably by faults. North of the Tagus a fault cuts off the tertiary 

 strata at Oeiras, the Almada beds forming one bank of the stream, 

 and the Hippurite limestone the opposite ; but the strata of each 

 deposit are horizontal. In Lisbon the Almada beds rest uncon- 

 formably on the Hippurite limestone ; but between the city and Ver- 

 delha, conformably on the lower tertiary conglomerate. In the band 

 ranging from St. Ubes by Palmella towards Aldea do Meco, they 



