THE GEOLOGY OF GIBEALTAH. 509 



Front, and passes westward to the Old Mole Head. At the eastern 

 end of the section the limestone dips a little north of west at angles 

 of from 12° to 20°. Further west the strata gradually curve to a 

 higher angle, and finally dip under the shale at an angle of about 

 83° on the ground between the Grand Casemate Square and the 

 Inundation. 



Section No. II., from Catalan Bay across Middle Hill to Wellington's 

 Front, very closely resembles Section No. I. in the arrangement of 

 strata both of limestone and shale. The direction of the strike, 

 however, has gradually curved, so that here the dip is about 15° 

 south of west. Mr. Smith accounts for this change of dip by 

 inferring the existence of a fault across the ridge. Of this fault, 

 however, we could find no trace, but were able to follow the beds 

 continuously from the one line of section to the other. It will be 

 noticed that in Section No. II. the limestone and shale where they 

 join are still nearly vertical. 



Section No. III. crosses the ridge at St. Michael's Gate at the east 

 end of Charles V.'s Wall, and passes through the Alameda Gardens 

 to the sea a little north of Careening Bay. The south-westerly 

 dips of the limestone on the ridge, on either side of this section, 

 vary from 47° to 65°. The shales that overlie the limestone are 

 concealed by the red superficial sands of the Alameda Gardens, but 

 are well seen in a vertical position, at low tide, at the north end of 

 Careening Bay, between the breakwater and the fortifications. 



Section No. IV. crosses the ridge at O'Hara's Tower, and passes 

 westerly to the sea between the New Mole Head and Eosia Bay, 

 near which it is believed to cross a fault, which throws the shale 

 down on the north-east against the limestone. At and near 

 O'Hara's Tower the westerly dip of the limestone is even higher 

 than that of the limestone at the top of the ridge in Section No. III. ; 

 for near O'Hara's Tower it ranges from 65° to 75°, and finally dips 

 under the shales and intercalated grits at the Engineer Boad, about 

 150 yards east of the Mount. 



With regard to these Sections (I., II., III., and IV.), it will be 

 observed that on the east, below the precipitous part of the Eock, the 

 limestone is in places unconformably overlain by limestone-agglome- 

 rate, on which lie the blown sands and loose rock-debris of Catalan 

 Bay and Sandy Bay. 



On the west, the ground immediately below great part of the 

 town, we were informed by Mr. Eoberts, consists of superficial 

 sand (which has been proved when excavating for foundations), and 

 which is similar to that so well seen in the Alameda Gardens, where 

 at its eastern edge it seems to rest on limestone- agglomerate, in the 

 manner shown in Section No. III. 



On the north side of Section No. IV. the limestone-agglomerate, 

 from 50 to 100 feet thick, overlies a large portion of the shale 

 between the New Mole Parade and Europa Main Eoad, and is 

 continued further south to the sea between Eosia Bay and the New 

 Mole Head. 



Between the main mass of the limestone of O'Hara's Tower and 





