Page:Transactions of the Geological Society, 1st series, vol. 3.djvu/35

 to see how by the wearing out of that vein the excavation has been formed, having subsequently acquired its present degree of ornament 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 probable 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 solutions 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 agitation 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 regularly 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.