4?8 Brigadier Silvertop^s Sketch of the Tertiary Formation 



ral low escarpments, formed by alternating horizontal strata of 

 coral sand, zoophytical freestone, and loosely aggregated quartz- 

 ose sandstone, border the road to Carbonera, studded with ter- 

 tiary testaceous remains of Balani, Echinus, Clypiaster, Ostreae, 

 and different species of Pectens, the latter in predominating num- 

 bers. There is subsequently a slight descent to the beach, 

 which, bordered by the tertiary tract, is followed to the village 

 of La Carbonera, 



In a little hollow, or dry ravine, which terminates on the 

 beach about a mile before reaching the village, a bed, or mass, 

 of pearlstone, containing numerous imbedded nodules of dark 

 bottle-green blackish obsidian, is observed, the upper part of the 

 hilly ground on each side of the hollow being composed of the 

 tertiary beds that are spread over an extensive area in the im- 

 mediate vicinity of this little seaport. (See Sect. 12. PI. III.) 



La Carbonera, — This village is situated at the distance of 

 about 100 yards from the beach, in a denudation of the tertiary 

 tract that has been followed along the coast from San Pedro. 

 The beds of this formation, which generally cover and conceal 

 the subjacent volcanic rocks over a considerable area in their 

 neighbourhood, extend along the coast about three miles beyond 

 La Carbonera, when they abut against a ridge of mica-slate, 

 called La Sierra di Cabrera, which descends to the beach, and 

 forms the boundary to the former towards the north-east. It may 

 therefore be stated, that they form a band of about twenty miles 

 in length, and from four to six in breadth, which borders the 

 Mediterrannean shore from the little seaport of San Pedro to 

 La Sierra di Cabrera. 



Constituting the high hill immediately to the north of the 

 latter village, over which the road to Carbonera was followed, 

 and which, from its long flat summit, is termed La Mesa (Table) 

 de San Pedro, the remaining portion of the band forms a low 

 broken hilly tract, characterised by one or two more elevated 

 tabular eminences, and particularly by La Mesa de Roldan. 



This tract presents, generally, a dry barren aspect, except in 

 some little denudated hollows, where the decomposed materials 

 of the tertiary beds, mixing with the detritus resulting from the 

 decomposition of trachytic rocks, upon which the former rest, 



