FIG. 11.-Brig o' Trams, Wick. Cliffs of Old Red Flagstone, showing how the inward inclination of the precipices is determined by lines of joint, and how the faces of rock are etched out by weathering along the lines of bedding.

1864, 'contains more than 500 tons, and is known as Charlie's Stone. Others varying in bulk from 100 to 5 tons or less lie by hundreds, piled up in all positions in high and long ridges, which, before the march of improvement began in the district, extended far into the field above the cliff.1 Near the old limekiln, South Head, similar large blocks of sandstone have been moved by the gales of the last three years. The great storm of December 1862 in particular distinguished itself by the havoc which it wrought along these shores. It swept the sea over the north end of the island of Stroma, which lies in the Pentland Firth,2 and redistributed the ruin-heaps there. The waves ran bodily up and over the vertical cliffs on the west side, 200 feet in height, lodging portions of the wrecked boats, stones, seaweeds, etc., on the top. They rushed in torrents across the island, tearing up the ground and rocks in their course towards the old mill at Nethertown on the opposite side. This mill had often before been worked by water collected from spray thrown over these cliffs, but never had such a supply been furnished as by this gale. One curious phenomenon was noticed at the south end of Stroma; the sea

1 This mass of ruin was noticed by Hugh Miller, who suggested that it might have been produced by the stranding of icebergs. Mr. Peach, however, remarked that there is every reason to believe it to be the work of the sea, and even now an occasional stone is added to the pile-a block at least half a ton in weight, about the year 1863, was torn up from its position fifty feet above the sea-level.

2 The spring tides of the Pentland Firth run at a rate of 10.7 nautical miles in the hour, and are probably by much the most rapid marine currents round the British Islands. Yet that they do not of themselves produce any appreciable abrasion of the coast-line is shown by the coating of barnacles and sea-weed on the rocks even at low water. As currents, their power by mere friction is probably nil; but when they are aided by powerful winds they lend a prodigiously accelerated impetus to the ordinary wind-waves. Hence the incredible force of the breakers in these northern seas.

there came in such a body between the island and the Caithness coast, that at intervals it rose up like a wall, as if the passage was too narrow for the mass of water which,

FIG. 13.-The Old Man of Hoy, Orkney. A stack of Upper Old Red Sandstone, 600 feet high, having at its base a zone of volcanic rocks which in turn rest upon the edges of tilted Lower Old Red Flagstones.

forced onwards from the Atlantic between Holburn Head on the Caithness shore and the Old Man of Hoy on the

Orkney side, passed bodily over the cliffs of Stroma. The effects of this terrific gale will long be remembered. Some time after its occurrence I was on Stroma and along the Pentland Firth side, and was deeply struck with the ruin spread around. The huge masses that had been moved exceeded all I had ever seen before. With this evidence, added to a long experience of storms, I am compelled to believe that the ruin of cliffs and the heaping-up of torn rock-masses have been effected by the sea when agitated by storms, and not by icebergs.'

A few years ago on the northern coast of Caithness I observed an interesting proof of the inroads of the sea upon the hard flagstones of that iron-bound shore. A 'brough' or 'Pict's House,' which, of course, had been originally entire, and had, no doubt, been built near the edge of the cliff for safety, was deeply trenched by the advance of a narrow gully in the precipice.

Leaving the dark flagstone cliffs and stacks of Caithness, we cross the wild tides of the Pentland Firth, and find ourselves among the rocky fjords and voes of the Orkney and Shetland Islands. There the power of the sea comes before us even more impressively. The intricate indented coast-line, worn into creeks and caves and overhanging cliffs; the crags, and skerries, and sea-stacks (Fig. 13), once a part of the solid land, but now isolated among the breakers; the huge piles of fragments that lie on the beach, or have been heaped far up above the tide-mark, tell only too plainly how vain is the resistance even of the hardest rocks to the onward march of the ocean. The rate of waste along some parts of these islands is so rapid as to be distinctly appreciable within a human lifetime. Thus, in the chain of the Orkneys, the Start Point of Sanday was in 1816 an island every flood tide; yet even within the memory of