SMITH ON GIBRALTAR. 43 



upon the former changes which the rock must have undergone sub- 

 sequently to its first upheaval. The most important of these is a 

 red sandstone containing recent marine shells : on the south-east it 

 attains a thickness of not less than 300 feet : it is formed of water- 

 worn grains of quartz cemented by the calcareous matter deposited 

 by the water which percolates through the superincumbent rock ; it 

 is extremely hard and tough, and is used in preference to the se- 

 condary limestone for lining the embrasures. The next in import- 

 ance is the breccia which covers the flanks of the mountain. It is 

 chiefly comj)osed of great and small fragments of the limestone ce- 

 mented in the same manner as the sandstone. We also find masses 

 of soil and mud similarly cemented, and in these the bones and shells 

 of land animals have been found. They form the well-known bone- 

 breccia of Gibraltar, some part of which must be of great antiquity, 

 as it contains the bones of extinct animals ; other parts of it are so 

 modern as to contain the remains of man and works of art. The 

 bone-breccia has been discovered in various parts of the rock, but 

 the principal locality in which it occurs is a fissure in the face of the 

 cliff" at Rosia Bay. In scarping the rock for the purpose of making 

 it more inaccessible, much of the bone-breccia has been removed, but 

 enough remains to show its origin. It is lodged in a fissure which 

 has evidently been connected with a cavern, the habitation of car- 

 nivorous animals ; the floor, like that of the present open caves, has 

 been formed by the dust of vegetable soil, blown into them during 

 the dry season : this has become mixed up with fragments and mi- 

 nute splinters of bone — the remains of the prey of its former inha- 

 bitants. A land-flood has swept this bony mud in a semi-fluid state 

 into the fissure, where it is now found. The direction of the flow can 

 be distinctly traced. The splinters, instead of being arranged hori- 

 zontally, are generally vertical, or rather parallel to the sides of the 

 fissure ; the mud has in time been indurated into breccia by calca- 

 reous infiltration, and afterwards cracked across by some of the num- 

 berless shocks to which the rock has been exposed while this trans- 

 verse fissure has in its turn been filled with stalagmite. Major 

 Imrie, who has described the geology of Gibraltar in the Transac- 

 tions of the Royal Society of Edinburgh, observed this circumstance, 

 and inferred from the septa or divisions thus formed that the fissure 

 had been filled at different periods. This however is not the case ; 

 for not only is the flow uninterrupted, but a pebble has been cracked 

 across, one half of which is above and the other below the division. 

 There are larger fragments mixed with the splinters, upon one of 

 which I observed the marks of the teeth of some animal. The cave 

 which has furnished the bony matter no longer exists, but this can 

 excite no surprise where so many causes of ruin have occurred, and 

 in point of fact this locality forms part of the great landslip to be 

 afterwards described. I have no additions to make to the list of 

 animals whose bones have been found in this breccia, except those 

 of the cave -bear and the fossil elephant. By permission of tiie Go- 

 vernor I made an excavation in Martin's Cave, but with no other 



