THE GEOLOGY OF GIBRALTAR. 525 



be seen even now standing ont in the sea at some little distance 

 from the shore. Bnt the best evidence of the agglomerate having 

 been subjected to marine erosion is afforded by a number of hori- 

 zontal terraces or platforms which have been excavated in it, and 

 which precisely resemble those that are cut in the face of the lime- 

 stone-cliffs and slopes as already described. 



The terraces referred to are shown in profile in Section IY. The 

 lowest forms the New Mole Parade, and reaches 50 feet above the 

 sea, thus corresponding in elevation to the old beach with shells 

 that was once visible at Europa Point. The next terrace occurs 

 behind the South Grand Store, at a height of 75 feet or thereabout, 

 and is probably the equivalent of the 70-feet beach which Mr. Smith 

 has recorded as rising behind the 50-f eet beach at Europa. The third 

 platform in ascending order is the flat occupied by the South Bar- 

 racks, a terrace which is 330 feet in width, and rises from 120 feet 

 or so to 140 feet above the sea. This height agrees with that of 

 the broad Europa Plateau. From this terrace the ground rises with 

 a somewhat rapid gradient to the fouith terrace, which forms the 

 gentle slope near the Mount that is traversed by the Ghiarda Main 

 Road. This sloping surface corresponds in elevation to the raised 

 beach shown at the east end of the section (Section No. IY.), and to 

 the similar platform with superimposed marine sandstone near No. 

 4 Europa Advance Battery. The height is 260 feet or thereabout 

 above the sea. 



Mr. Smith got recent marine deposits at a height of 700 feet 

 above the sea ; and he inferred from the worn aspect of the Eock, 

 and the presence of caves at yet higher levels, that the whole pro- 

 montory had probably been submerged within recent geological 

 times. The caves in question, however, are not of marine origin ; 

 they are of the usual irregular character, descending to great depths 

 and, as they are followed downwards, receiving or sending out 

 lateral winding branches, just as is the case with limestone-caves 

 and galleries elsewhere. From the view we obtained of the caves 

 at the present sea-margin, immediately underneath the great cliff 

 that descends from O'Hara's Tower, we could have little doubt that 

 even these were not entirely the result of marine erosion, but had 

 originated in the same way as the others, the sea having merely 

 exposed them in the process of cutting back its cliff. The occur- 

 rence of caves, then, at a higher level than 700 feet cannot be taken 

 as a proof of greater submergence than that. Nor is the honey- 

 combed and worn aspect of the Rock any evidence of marine action, 

 ordinary weathering being quite enough to account for all the ap- 

 pearances presented. At the same time it is of course possible that 

 submergence may have considerably exceeded 700 feet. If it did 

 we might expect to come upon patches of shell-bearing sandstone 

 lying in protected crevices of the limestone, like those which were 

 laid bare, at the time of Mr. Smith's visit, in the process of quarry- 

 ing and scarping the limestone. We did not observe any, however ; 

 but a more minute search than we were able to make might be re- 

 warded with success. 



