THE GEOLOGY OF GIBRALTAR. 523 



it shows a reddish tinge. It is somewhat coarse in texture, passing 

 into a grit, and appears to be made up chiefly of comminuted frag- 

 ments of limestone, quartz, and shells — none of the latter being 

 large enough to enable us to tell the species. We noticed, however, 

 fragments of Echinus-tests ; and there can be no question that the 

 deposit is a marine accumulation, similar to the shelly sand which 

 is at present gathering here and there in shallow water along the 

 coast. Mr. Smith, indeed, mentions that he obtained from the beds 

 Patella ferruginea, a recent Mediterranean species. Beds of pre- 

 cisely the same character are well exposed at No. 4 Europa Advance 

 Battery, where they dip outwards from the high cliff behind at an 

 angle of 27° or thereabout. Just beyond the battery is an old sea- 

 worn cave, in which the same sandstone-beds appear to form a con- 

 siderable thickness, as they are piled up against the steep cliff-wall 

 from near the present sea-level to the platform of limestone on which 

 the battery stands, a height of 260 feet. Mr. Smith mentions the 

 occurrence of similar deposits in and near old sea-worn caves at 

 heights of GOO and 700 feet above the present sea-level ; but these 

 we were not fortunate enough to come upon. 



The sandstone and grit evidently owe their induration to the per- 

 colation of water holding carbonate of lime in solution ; and it was 

 curious to trace in this modern rock certain appearances which have 

 already been referred to in connexion with the main limestone. 

 Towards the top of the sandstones, angular fragments of limestone, 

 some of them several feet in diameter, begin to show themselves ; 

 and these can usually be distinguished at a glance from the matrix 

 in which they lie imbedded. Now and again, however, the shelly 

 grit or sandstone quite loses its gritty character, becoming fine- 

 grained and almost compact ; and then it so closely resembles in its 

 lithological aspects the main limestone as to be with difficulty dis- 

 tinguished from the fragments of the latter, which it encloses. 



It is highly probable that such sandstones and grits extend more 

 or less continuously from No. 4 South, by Nos. 3 and 2 Europa Ad- 

 vance Batteries, up to and beyond the Governor's Cottage; but they 

 are concealed under heavy masses of limestone-agglomerate, as we 

 shall point out presently. The sandstone-beds rest upon the sea- 

 worn platform which we have described as extending from Europa 

 Elats past the Governor's Cottage to No. 3 Europa Advance Battery. 

 North from that point the Europa level becomes obscured ; but it 

 doubtless continues under the agglomerate until it meets the steep 

 cliffs that plunge down to the sea just beyond No. 4 Europa Advance 

 Battery. There are also indications of a higher platform of lime- 

 stone being concealed below the sandstone and overlying agglome- 

 rate which form the slopes that dip outwards from the base of the 

 cliffs behind Monkey's-Cave Road. The height of the level referred 

 to can hardly be less than 250 feet above the level of the sea. A 

 little further to the north a well-marked platform appears excavated 

 in the steep cliff. This old sea-margin is shown in Section IV. : it 

 is capped, as usual, with limestone-agglomerate. 



At Prince's Lines (North Front) another sea-worn shelf of lime- 



