OF GIBRALTAR. 19 



origin. There is another peculiarity in the geological 

 history of the rock, which its external surface indicates, 

 and which ought not to pass unnoticed, even in this 

 imperfect sketch, viz. the wasting action of the sea. 

 This is ohservable on almost every part of the rock, 

 and it is strongly indicated by the cliffs and terraces 

 which could only have been formed by the action of 

 water. The sea also appears to have impressed the 

 sides of caves and fissures and pot-like cavities of 

 even the highest parts of the rock with " water- worn 

 marks," and some of the smaller caves appear to have 

 been formed by the wasting action of the sea an 

 operation which is still observable at the present level 

 of the sea. These facts prove beyond a doubt that the 

 sea stood at these levels at different periods of its geo- 

 logical history. Mr. James M c Gregor of the Medical 

 Staff, was the first, I believe, to point out the beds of 

 oyster-shells in the higher parts of the rock ; one of 

 these beds, situated at Europa above the Engineers* 

 quarters, is formed of shells resembling those of 

 oysters at present found in the Mediterranean, so that 

 it would appear that the sea stood at these high levels 

 at a comparatively modern date. Two new deposits of 

 shells have lately been laid open at the heights of 

 seventy and eighty feet, near Europa mess-room. This, 

 Mr. Smith considers one convincing proof among 

 others, that the sea stood at these two respective levels 

 at two distinct periods ; and, according to him, these 

 shells are all of the post-tertiary epoch. 



Having brought to a conclusion this brief sketch of 

 the Geology of Gibraltar, it remains for me to treat 



c 2 



