Mineralogy^ of Sky. 27 



to see how by the wearing out of that vein the excavation has been 

 formed, having subsequently acquired its present degree of orna- 

 ment by the infiltration of carbonat of lime in solution. When 

 we consider the great depth of this cave and its distance at 

 present from the sea, we are inclined to inquire by what means 

 / so extensive an excavation could have been formed, and how 

 the rock which has fallen from it has been disposed of. It is pro- 

 bable that the depth of water at the face of the cliffs was once such 

 as to allow of the ready access of the sea to them, and that at this' 

 period the excavations so numerous on this shore were produced. 

 The subsequent accumulation of rubbish formed by its action, has 

 in later times produced the slope or shore which now excludes it 

 from further access, and protects the cliffs from further demolition. 

 In the little excavations which are found in the floor of this cave 

 we have the means of seeing the process by which the formation of 

 calcareous spar takes place, the crystallization being carried on in a 

 solution of the carbonat of lime, precisely as it is in the saline so- 

 lutions in our laboratories. All these small pools are filled with 

 groups of crystals, in a state of constant augmentation, but of very 

 irregular forms. Doubtless these forms must be affected by the agi- 

 tation which the falling drops occasion in the solution ; and it is in 

 all probability owing to some circumstances of this nature, constant 

 in the same place but varying in different ones, that crystals of one 

 form are found to affect certain places, while in others they regu- 

 larly assume some other modification. As it offers no novelty to the 

 mineralogist, and belongs to a class of geological facts by no means 

 uncommon, it is unnecessary to enter into any further details 

 respecting it. Such are the principal circumstances which I had an 

 opportunity of remarking, and which appeared most worthy of notice 

 in the general face of the island. 



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