42 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



south, and three-quarters of a mile in breadth. It is terminated on 

 the north by a perpendicular cliff 1250 feet in height; its greatest 

 elevation is 1470 feet, and its southern extremity is marked by a 

 triple series of cliffs and terraces. The elevated part of the rock 

 which occupies the northern half of the peninsula is divided into 

 three distinct eminences by gaps in the summit and ravines at the 

 sides. The most northerly eminence is called by the Spaniards 

 * Salto de Lobos,' and ' Wolf's Crag' by the English ; the precipice is 

 called the North Front, and the height above it the Rock-gun, from 

 the gun perched on its summit. The hill in the centre is called 

 Middle Hill or the Signal Station, and the southern height ' Pan 

 d'Assucar' or the Sugar-loaf, but more commonly O'Hara's Tower. 

 To the south of this there is a plain called Windmill-hill Flats, about 

 400 feet above the level of the sea. This is bounded by an escarp- 

 ment and succeeded by a second and lower plateau called Europa 

 Flats ; and at the southern extremity of the promontory there is, or 

 rather was, a third terrace separated by a sea- worn cliff from the 

 Europa Flats ; but the cliff is now concealed by fortifications, and 

 the terrace by a glacis. 



1. 



N. 



s. 



Lower 



Europa 



Windmill- 



O'Hara's 



Middle 



Rock 



Europa. 



Flats. 



hill Flats. 



TOWCT. 



Hill. 



Gun. 



In the above diagram is represented the general appearance of the 

 western face of the rock. The beds of limestone in the elevated part 

 dip to the west, but from Windmill-hill Flats, southwards, they dip to 

 the east. About halfway up the western side of the elevated part, 

 there is a precipice parallel to the ridge on the summit or axis of the 

 rock ; at the base of this precipice there is a plain of stratified siliceous 

 sand, called the red sands, upon which the town is built and the 

 esplanade and Alameda or public garden formed. On the shore at 

 the western base of the rock, and parallel to its axis, there is a series 

 of beds of highly indurated shale ; these are nearly vertical, and se- 

 parated as they are from the stratified limestone beds by sands or 

 breccia, it is impossible to determine whether they lie over or under 

 them. The same may be said of beds of secondary sandstone which 

 also occur on the west side of the rock, but are not seen in contact 

 with the limestone : this however is not a point of any geological 

 consequence, as they all evidently belong to the same formation. 



No rocks of the miocene tertiary period, although these are so 

 largely developed in the immediate neighbourhood, occur in the pro- 

 montory of Gibraltar ; neither are there any newer tertiary deposits, 

 unless we call the breccia, in which the bones of the cave-bear and 

 fossil elephant have been found, tertiary. The post-tertiary rocks are 

 numerous, and of great geological interest from the light they throw 



