he must have noticed an exact counterpart to these appearances. When the waters have subsided, the overflowed parts are seen to be covered in many places with sand. Wherever a pebble occurs along the surface of this sand, it has invariably a hollow before it on the side facing the direction whence the stream is flowing, and a long tail of sand pointing down the channel. If we watch the motion of the water along its bed, the denuding agency may be seen actively at work. Every pebble that protrudes above the shallow streamlet arrests the course of the current, which is then diverted in three directions. One part turns off to the right hand of the pebble, and cuts away the sand from its flank; another part strikes off to the left, and removes the sand from that side; while a middle part descends in front of the pebble, and, by a kind of circular or gyratory movement, scoops out a hollow in the sand in front. Behind the pebble the water is pretty still, so that the sand remains undisturbed, and is further increased by the accumulation above it of sediment swept round by the lateral currents. Now, in place of the supposed stream, let us substitute the ocean with its westerly current--for the pebble, a great trap-hill--for the sand, easily friable shales and sandstones, and we have exactly the condition of things which produced crag and tail. This process of destruction must have been in progress during many geological ages. We may suppose, that in that time the land often changed level, sometimes rising far above the sea, and sometimes sinking deep below it. We can well believe that the surface would often be covered with vegetation; that plants, widely differing from those which are now indigenous, clothed its hill-sides and shaded its valleys; and that animals of long extinct forms roamed over its plains or prowled amid its forests. When the country, in the lapse of centuries, sank beneath the sea-level, all trace of these scenes would eventually be effaced. The westerly currents would soon recommence the process of degradation, uprooting the forests, devastating the plains, wearing down the hills, and scooping out the valleys; and so, when the ocean-bed, in the course of ages, became again dry land, it would arise "another and yet the same." The little valley, where once, perchance, the mastodon used to rest his massive bulk amid a rich growth of ferns, shaded by the thick umbrage of coniferous trees, would emerge a deep glen with bare and barren rocks on either side; the site of the hill whereon herds of the gazelle-like anoplothere were wont to browse, might reappear a level plain; the low-browed rock, under whose shadow the ungraceful palæothere used of old to rest from the heat of the noon-tide sun, might emerge a beetling crag shooting up several hundred feet over the valley. It is by this repeated elevation and submergence, carried on for many ages, that our country has acquired its present configuration.