THE GEOLOGY OF GIBEALTAE. 



529 



Battery, the sandstone contains no blocks of limestone, either angu- 

 lar or rounded ; while in the old sea-clefts which are seen under- 

 neath that Battery angular fragments appear likewise to be absent 

 from the horizontally-bedded sandstones which there abut against 

 the cliffs. Immediately upon the somewhat steeply-sloping (27°) 

 surface of the sandstones at No. 4 Europa Advance Battery comes a 

 thick mass of agglomerate, as shown in the section (fig. 10, p. 527). 

 It will be remembered that at Prince's Lines a similar section was 

 laid bare, only that at that place the agglomerate was separated from 

 the limestone platform by a thin bed of pebbly conglomerate. 



From these and other like facts it may be inferred that after the 

 limestone platforms and plateaux had been eroded, and sand and 

 grit had been deposited upon them here and there in considerable 

 quantities, angular blocks began to be detached from the heights 

 above, and to plunge downward into the yielding deposits. Certain 

 considerations would seem to render it highly probable, however, 

 that before these blocks began to fall the sand-beds had been ele- 

 vated above the sea. The sandstones which rest upon the limestone 

 platform of No. 4 Europa Advance dip at the high angle of 27° out- 

 wards from the cliff; and all the appearances visible in that locality 

 lead to the inference that the sandstones there form a long sloping 

 bank underneath the agglomerate, a bank resembling the great sand- 

 slopes of Catalan. After the sands had been lifted out of the sea, 

 the atmospheric forces would set to work upon them, and it is not 

 difficult to see how in no long time they would come to assume a 

 sloping surface. Their upper portions would thus be rearranged, 

 and the sand at and near the surface would have a dip corresponding 

 to the steep inclination of the bank. We see precisely the same 

 appearance of a steep outward dip in the blown sands of Catalan ; 

 and any one who shall compare the deposits of these two places will 

 be struck with the close resemblance not only in the matter of 

 bedding, but also in regard to their composition ; for both are made 

 up of the same coarse gritty materials. Now at Catalan some por- 

 tions of the blown sand and grit are indurated by infiltration, while 



Fig. 12. — Section at Monkey's- Cave Battery, 260 feet above the sea. 



s. Shelly grit. 



a. Limestone-agglomerate. 



2n2 



