Chap, i.l CAVERNS. ig 



ments cemented together, as usually occurs in coral islands. 

 The sand rock contains various fossils, most abundantly a land 

 snail {Helix) now abundant in the islands, and a much larger 

 one, now extinct, but closely resembling the present species in 

 other respects than size. The bones of turtles and birds are 

 also found in the rock, and all the common marine shells of the 

 islands. The rock, when exposed, is honeycombed by the 

 action of the rain and that of sea water, and on the coast its 

 surface has a remarkable corroded appearance. It is eaten into 

 cup-like hollows all over, separated from one another by 

 extremely sharp projecting points and edges of thin laminae, 

 which break with a crackling noise under the feet. In some 

 places on the coast the rock has been left by denudation pro- 

 jecting in isolated pinnacles and peaks of fantastic form. 



The surface of the rock is not only honeycombed by the 

 action of rain, but hardened by re-deposit of carbonate of lime ; 

 and a fresh surface exposed to the weather soon becomes 

 covered with a hard film. Extensive caverns exist all over the 

 islands, undermining the rock in all directions, and filled at the 

 bottom with water, which, in caves near the sea, rises and falls 

 with the tide and is salt. At Paynter's Vale Cave the water is 

 only brackish, so that the communication underground with the 

 sea must be slight. Such caves must necessarily result from the 

 consolidation of masses of loose sands by means of the percola- 

 tion of rain water. The carbonate of lime taken up must leave 

 cavities unless the whole mass were to shrink gradually ; but as 

 the outer or upper layers receive the water first, they become 

 consolidated, and hardened more thoroughly than the inner. 

 Subsequently, these outer layers being hardened, the water 

 ceases to take up so much lime from them, but passes through 

 cracks and chinks, to dissolve away the softer interior, which 

 sinks and falls in. A cave is the result, on the roof of which 

 stalactites form at once. 



The falling in of the roofs of ancient caves gives rise to many 

 peculiar features in the landscape of Bermuda. The stalag- 

 mites at Walsingham Cave are far under water, proving a 

 sinking of the floor of the cave which- might possibly be 

 supposed to be local, due to the giving way of some hollow 

 beneath ; but since the same condition is to be seen in nearly 

 all the caves, and there is the further evidence of the sunken 

 bed of lignite, there seems no doubt that there has been a 

 general sinking of the island in comparatively recent times. In 

 some places on the coast of Bermuda are reefs composed by 

 Serpulte, which were called by Nelson Serpuline reefs. These 

 often form regular circles or tiny atolls, as it were, about 20 to 

 30 feet in diameter. The form evidently results from the fact 



