We continue our ascent. A scrambling walk through briars and hazel-bushes, sometimes on rocky ledges high among the cliffs, sometimes among the prostrate blocks that dam up the stream, brings us at last full in front of a sparkling waterfall that dashes over a precipitous face of rock some twenty feet high. The appearances observable here deserve a careful attention. Our eyes have not been long employed noting the more picturesque features of the scene ere they discover that the dark-brown band of rock forming the summit of the ledge over which the water tumbles is continuous all round the sides of the dell. There is consequently no break or dislocation here. Approaching the cascade we note the rock behind it so hollowed out that its upper bars project several feet beyond the under ones. In this way the body of water is shot clear over the top of the cliff without touching rock till it comes splashing down among the blocks in the channel. And yet this hollowed surface is never dry; the spray of the fall constantly striking on it keeps it always dank and dripping. In some parts the rock stands out bare and worn, while on the less exposed portions there gathers a thick green scum which is replaced on the drier ledges by the soft cellular leaves of the liver-wort. Now our examination of the influence of percolating water upon even the hardest rocks teaches us that this moist soaked surface is just the very best condition for favouring the decay of the rock. Nay more, the green vegetation that mantles over the stone serves to prevent the water from running off too rapidly, and keeps the rock in a still more moist state than would otherwise happen. So that the portion of sandstone behind the cascade comes to be in a still more favourable situation for speedy decay than the ledge over which the water is rapidly driven. We can see, therefore, how in the lapse of years the corrosion may go on until the upper projecting part of the cliff loses its support and falls with a crash into the rocky pool below, while the form of the waterfall becomes thus greatly altered, and new surfaces are exposed to the wear and tear of the stream.