34 MR. H. DYKE ACLA.ND ON A. [^ e ^« I9°4 5 



floor, and it would evidently require the removal of a large amount 

 of rubble and breccia to reach it. 



Such is a brief description of the general character of the cave. 

 It remains to point out one or two of its more interesting features 

 from a geological point of view. 



Gibraltar, as is well known, has many examples of both Assure 

 and marine caves at very various heights above sea-level, St. Michael's 

 Cave on the western side being perhaps the most famous of the first 

 kind, and the caves on the eastern coast-line of the second. There 

 can be no doubt that the upper gallery in the cave just described 

 is wholly or partly of marine origin, from the character of the 

 concave and unfissured end, the sand and pebbles formed beneath 

 the stalagmite-floor, and the fact that the floor is horizontal. It is 

 equally evident that the main hall and lower gallery originated 

 in a fissure, and were subsequently exposed to the action of the sea. 

 The presence of echinids of the same species as those which still 

 exist in the Mediterranean makes it probable that the upper 

 gallery is the older, and that the Rock has been elevated since the 

 upper gallery received in a great measure its present form. 



The band of honeycombing is evidence that the water must have 

 remained at the same level in the cave for some considerable time. 

 The edges of the pittings are so sharp that they cannot have been 

 exposed to the action of moving water for any lengthy period. They 

 are not seen in the shaft in the lower gallery below the level of 

 the present floor, and the side of the cave at that point has the 

 appearance of having been planed down by the sea. It is not likely 

 to have been fresh water, as it is difficult to see whence any con- 

 siderable stream of the latter could have come, or whither it could 

 have gone. 



The striations on the south side of the main hall may be due to 

 the action of blown sand. Very similar markings of recent origin 

 are to be now seen on the sides of the entrance to the well-known 

 Monkey's Cave, which lies a short distance to the south, and there 

 a heap of sand lies in the cave. If the striations in the main hall 

 are due to this cause, it shows that there must have been a large 

 opening to the cave on a much lower level than the present one. 



By the kindness of Dr. A. Smith Woodward, F.R.S., and Dr. F. 

 A. Bather, M.A., the echinids have been identified. They are Stron- 

 gylocentrotus lividus, a species still common in the Mediterranean. 

 The cave must therefore have been open to the sea at a com- 

 paratively-recent geological period. The bed of sand and PJw/as- 

 bored stones in which they were found was about 4 feet thick, above 

 which are 11 feet of rubble, sand, and stalagmite. The rubble may 

 be attributed to falls from the roof. 



The breccia brings us to the last page in the history of the cave 

 until its recent discovery. I believe its origin to be twofold. It 

 will be observed that the floor of the main hall slopes considerably 



