by beetles, chirupped over by grasshoppers and crickets, and crawled over by four-footed reptiles, that united in their structure the lizard and the frog. But of the general grade and proportions of its denizens we still remain in ignorance. From all that yet appears, the scenery of these forests must have been dark, silent, and gloomy, buried in a solitude that was startled by no tiger's roar, no cattle's low, and neither cheered with the melody of birds nor gladdened by the presence of man. We have lingered, perhaps, too long over the remains of these old carboniferous animals. But the delay may be not without its use if, by thus bringing before us some of the more marked points in the structure of creatures that for ages peopled our planet, it broaden our view of creation; and by lifting the curtain from off a dim, distant period of our world's long history, it show, amid all diversities of arrangement, and all varieties of form, still the same grand principles of design, and the same modes of working as those which we can see and compare among the living forms around us. It is something to be assured that the race of man has been preceded by many other races, lower indeed in the scale of being, but manifesting, throughout the long centuries of their existence, ideas of mechanism and contrivance still familiar to us, and serving in this way to link the human era with those that have gone before, as parts of one grand scheme carried on by one great Creator. CHAPTER VIII. Sand and gravel of the boulder--What they suggested--Their consideration leads us among the more mechanical operations of Nature--An endless succession of mutations in the economy of the universe--Exhibited in plants--In animals--In the action of winds and oceanic currents--Beautifully shown by the ceaseless passage of water from land to sea, and sea to land--This interchange not an isolated phenomenon--How aided in its effects by a universal process of decay going on wherever a land surface is exposed to the air--Complex mode of Nature's operations--Interlacing of different causes in the production of an apparently single and simple effect--Decay of rocks--Chemical changes--Underground and surface decomposition--Carbonated springs--The Spar Cave--Action of rain-water--Decay of granite--Scene in Skye--Trap-dykes--Weathered cliffs of sandstone--Of conglomerate--Of shale--Of limestone--Caverns of Raasay--Incident--Causes of this waste of calcareous rocks--Tombstones.