114 Mr. D. Sharpe on the Geology of 



pands to a breadth of four miles ; and thence it may be followed along the narrow 

 valley which passes between Odivellas and Lumiar to Bemfica, where, turning to- 

 wards Lisbon, it thins out and gradually disappears near the gate of San Sebastiao 

 de Pedreira. 



At its northern extremity this deposit rests upon the red sandstone, but through- 

 out the remainder of its course upon basalt : the beds dip conformably under the 

 Almada formation at angles of 10° or 15° S.E., but the inclination increases in the 

 lowest beds to 30°. 



This formation is well displayed where it is crossed by the road to Canessas, 

 the beds there exposed, in a descending order, being as follows : — 



The lowest strata of the Almada formation. 



Marl. 



Soft limestone, containing pebbles of limestone and flint. 



Limestone, inclosing angular fragments and rounded pebbles of limestone, the whole forming a hard 



rock. 

 Calcareous beds, containing pebbles of limestone. 



flint. 



Sandstone, passing into coarse gritstone and rough conglomerate, with large siliceous pebbles. 



Sand and gravel. 



Clay and marl. 



Clay formed of the detritus of basalt. 



Decomposed basalt. 



Compact basalt. 



The thickness of the formation is here about 200 feet. 



Near Loures and Tojal there is less of the harder conglomerates, and a greater 

 proportion of marl, gravel, and the soft calcareous conglomerates. 



Many of the basaltic hills along the bank of the Tagus below Lisbon, are capped 

 with a bed of clay containing basalt in different states of decomposition, upon 

 which the Almada beds rest near Santa Catarina and San Joze de Riba-mar. 

 This clay and decomposed basalt are sometimes fifty feet thick, and are without 

 doubt of the same age as the similar beds near Loures and Odivellas, and must 

 be referred to this formation. (Pi. XV. Sect. 1, 3, 6 and 7.) 



I did not meet with the conglomerate south of the Tagus. I did not find any 

 organic remains imbedded in it. 



The separation between the tertiary and the secondary series can nowhere be 

 more distinctly marked than in the neighbourhood of Lisbon. The secondary 

 rocks were both disturbed and denuded previously to the deposition of the tertiary, 

 which lie not only upon the newest secondary formation, but also upon rocks of 

 very different ages. The separation between them is still further marked by an 

 immense mass of basalt which overflowed the secondary formations before the 



