the Neighbourhood of Lisbon. 1 23 



some large quarries at the village of San Pedro, from which I have taken its name. 

 At this spot the beds succeed each other in the following order : — 



Dark grey, compact limestone, several hundred feet thick. 

 Grey limestone, with slight traces of crystalline structure, in the 



lower part becoming granular 200 feet. 



Coarsely crystalline marble, white, or white and grey 100 — 



Irregularly crystallized calcareous spar, usually grey 100 — 



Calcareous spar, breaking into large crystals ; colour bluish-white. 

 Granite. 



The same gradual change may be traced around the Cintra hills, wherever the 

 limestone can be seen resting upon or approaching the granite. In some spots 

 the crystalline marble is quite equal in colour to the Carrara, but it is too soft 

 for use. 



The stratification of the limestone is hardly altered by the change of structure, 

 but the crystalline beds are thicker than the others. The alteration is very gra- 

 dual, the characters of each bed being uniform, and a slight change taking place 

 between it and the one next below. 



The strata dip from the granite at angles varying from 40° to 70° ; near San 

 Pedro they are considerably dislocated. 



Organic Remains. — T found in the limestone the casts of one univalve and one 

 bivalve, but too much crushed to admit of determination. 



6. Older Red Conglomerate. (PI. XIV. and PI. XV. Sect. 9, 11 and 13.) 



On the west of St. Ubes a coarse conglomerate rises into hills of considerable 

 height, in a position entirely unconformable to the neighbouring formations. There 

 is no clue to its place in the series, except that it is more ancient than all the sur- 

 rounding strata ; but as it does not occur near Cintra, there is no evidence of its 

 being older than all the formations just described in that district, for the altered 

 characters of the two lowest of those deposits make it impossible to compare them 

 safely with rocks elsewhere. In this uncertainty, I have left the account of the 

 formation to the end of the aqueous deposits ; expecting that it will hereafter be 

 found to be older than any of the strata yet noticed. 



The conglomerate usually consists of rounded pebbles from half an inch to more 

 than a foot in diameter, firmly cemented in coarse ferruginous sandstone, and 

 composed mostly of white or ferruginous quartz ; but pebbles of jasper and mica- 

 slate, and a few of limestone also occur. The harder beds have been used for orna- 

 mental work in most of the old churches about St. Ubes ; but the stone will not 

 take a good polish, owing to its unequal composition. 



The conglomerate forms the highest ridge of the Serra de Covoens, at the eastern 



R 2 



