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After the crushing was done the cracks in the Carboniferous Limestone were filled with water heavily charged with calcium carbonate, taken in solution from the rock, first from pulverized particles, and afterwards by percolation and contact with exposed surfaces.
The reason of this is evident. When there is a small proportion of the calcareous matter in the mass of sand which is pervious to steam and to the percolation of water, the calcareous bodies may be easily dissolved, and either carried away or dispersed in the mass; or even without being thus dispersed by means of solution, the calcareous matter may be absorbed by the siliceous substance of the stratum by means of fusion, or by heat and cementation.
They maintain their level by receiving fresh water at the head and by percolation through the beach, while most of them are connected with the sea. We noticed the usual feature, a long thatched barn of yellow clay school-cum-chapel. It is a tree of many uses.
During the slow upheaval and denudation of the lodes, they have been subjected to various chemical, hydro-thermal, and aqueous agencies, by which many of their contents have been re-arranged and re-formed, new minerals have been brought in by percolation of water from the surrounding rocks, and possibly some of the original contents have been carried out by mineral springs rising through the lines of fissures which are not completely sealed by the igneous injection, as the contraction of the molten matter in cooling has left cracks and crevices through which water readily passes.
It was certainly very curious and beautiful; evidently a huge cavity out of which the calcareous sand had been washed or dissolved, and whose walls, still to a certain extent permeable, had been hardened and petrified by the constant percolation of water charged with carbonate of lime.
We could hear it increasing in volume every moment. The torrent, which for a long time could be heard flowing over our heads, now ran distinctly along the left wall, roaring, rushing, spluttering, and still falling. Several times I passed my hand across the rock hoping to find some trace of humidity of the slightest percolation. Alas! in vain. Again a half hour passed in the same weary toil.
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