532 A. C. RAMSAY AND J. GEIKIE ON 



have been the bare desiccated ridge that it now is. The climate 

 was probably very genial, and vegetation must have been more 

 abundant, so as to have afforded food for the ibex, the bones of which 

 occur in great numbers at Genista ; and several of the other vege- 

 table-feeders were also in all probability regular denizens of the 

 place. Prom the presence of the African species, Messrs. Busk and 

 Falconer are quite justified in their inference that " there was a 

 connexion by land, either circuitous or direct, between the two con- 

 tinents at no very remote period." 



The next phase in the geological history of the Rock was its sub- 

 mergence. There is no evidence to show whether that was slowly 

 or rapidly effected as a whole. But certain considerations would 

 seem to lead to the inference that there were pauses in the move- 

 ment, during which some at least of the limestone-ledges were 

 eroded. It is difficult otherwise to account for the fact that certain 

 platforms of erosion, such as that near Monkey's Cave, are covered 

 with thick deposits of calcareous sandstone. These platforms could 

 not surely be eroded and covered with thick sand during one and 

 the same period of upheaval. It seems more likely that the ledge 

 at Monkey's-Cave Road was carved out during a pause in the subsi- 

 dence, and that afterwards it became buried under sand, either as 

 the land went down or while it was coming up again, or partly at 

 one time and partly at the other. Prom the presence of shells of 

 recent Mediterranean species in the sandstone-beds, we gather that 

 these deposits were laid down under conditions that could not have 

 differed much, if at all, from those which are now met with in the 

 neighbouring waters. 



After reelevation had lifted these sand-beds above the level of the 

 sea, and probably reunited the Rock to the mainland of Spain, the 

 unconsolidated sands were exposed to the action of the weather, and 

 gradually smoothed off into a more or less steep slope. At this time 

 the Rock seems to have been again visited by a mammalian fauna, the 

 remains of which occur in and underneath the more recent lime- 

 stone-agglomerates that overlie the old platforms or ledges of marine 

 erosion, as at Prince's Lines ; and probably also to the same period 

 maybe assigned some portion of the cave-breccias. At the same 

 time it is possible that the bones that occur under these beach- 

 obscuring agglomerates may be derivative. This is a point which 

 only future excavation will decide ; at present the evidence is in- 

 sufficient. It may be that the two continents were again united 

 after the depression, and that the African Mammalia reimmigrated. 

 In that case probably some portion of the cave-deposits may belong 

 to this second union of the continents. 



The great sand-slope at Catalan has generally been assigned ex- 

 clusively to the action of the wind ; and if this view be correct, then 

 the slope must date its origin to a time when a wide tract of low 

 ground existed to the east and north-east of the promontory. The 

 sand (which contains much quartz) cannot possibly have been 

 derived from the degradation of the limestone series of Gibraltar, 

 but, no doubt, results from the waste of coarse sandstones like those 



