breakwaters _were not_, the Atlantic _was_, and that its tempests, which in the present time can transport vast rocks for hundreds of yards along the exposed coasts of Shetland and Orkney, may have been the agent here in the transport of these huge pebbles of the Old Red conglomerate? "Rocks that two or three men could not lift," say the Messrs. Anderson of Inverness, in describing the storms of Orkney, "are washed about even on the tops of cliffs, which are between sixty and a hundred feet above the surface of the sea, when smooth; and detached masses of rock, of an enormous size, are well known to have been carried a considerable distance between low and high-water mark." "A little way from the Brough," says Dr. Patrick Neill, in his 'Tour through Orkney and Shetland,' "we saw the prodigious effects of a late winter storm: many great stones, one of them of several tons weight, had been tossed up a precipice twenty or thirty feet high, and laid fairly on the green sward." There is something farther worthy of notice in the stone of which the two boulders of the Dog-stack are composed. No species of rock occurs more abundantly in the embedded pebbles of this ancient conglomerate than rocks of the trap family. We find in it trap-porphyries, greenstones, clinkstones, basalts, and amygdalolds, largely mingled with fragments of the granitic, clay-slate, and quartz rocks. The Plutonic agencies must have been active in the locality for periods amazingly protracted; and many of the masses protruded at a very early time seem identical in their composition with rocks of the trap family, which in other parts of the country we find referred to much later eras. There occur in this deposit rolled pebbles of a basalt, which in the neighborhood of Edinburgh would be deemed considerably more modern than the times of the Mountain Limestone, and in the Isle of Skye, considerably more modern than the times of the Oolite.