tract equally moory which spreads over the gray flagstones, I marked, more especially in the hollows and ravines, where minute springs ooze from the rock, vast quantities of bogiron embedded in the soil, and presenting greatly the appearance of the scoria of a smith's forge. The apparent scoria here is simply a reproduction of the iron of the underlying flagstones, transferred, through the agency of water, to that stratum of vegetable mould and boulder-clay which represents the recent period.

I found the stack which I had been brought to see forming the picturesque centre of a bold tract of rock scenery. It stands out from the land as a tall insulated tower, about two hundred feet in height, sorely worn at its base by the breakers that ceaselessly fret against its sides, but considerably broader atop, where it bears a flat cover of sward on the same level with the tops of the precipices which in the lapse of ages have receded from around it. Like the sward-crested hammock left by a party of laborers, to mark the depth to which they have cut in removing a bank or digging a pond, it remains to indicate how the attrition of the surf has told upon the iron-bound coast demonstrating that lines of precipices hard as iron, and of giddy elevation, are in full retreat before the dogged perseverance of an assailant that, though baffled in each single attack, ever returns to the charge, and gains by an aggregation of infinitesimals, the result of the whole. From the edge of a steep promontory that commands an inflection of the coast, and of the wall of rock which sweeps round it, I watched for a few seconds the sea,-greatly heightened at the time by the setting in of the flood-tide, -as it broke, surge after surge, against the base of the tall dark precipices; and marked how it accomplished its work of disintegration. The flagstone deposit here abounds in vertical cracks and flaws; and in the line of each of the

many fissures which these form the waves have opened up a cave; so that for hundreds of yards together the precipices seem as if founded on arch-divided piers, and remind one of those ancient prints or drawings of Old London Bridge in which a range of tall sombre buildings is represented as rising high over a line of arches; or of rows of lofty houses in those cities of southern Europe in which the dwellings fronting the streets are perforated beneath by lines of squat piazzas, and present above a dingy and windowless breadth of wall. In course of time the piers attenuate and give way; the undermined precipices topple down, parting from the solid mass behind in those vertical lines by which they are traversed at nearly right angles with their line of stratification; the perpendicular front which they had covered comes to be presented, in consequence, to the sea; its faults and cracks gradually widen into caves, as those of the fallen front had gradually widened at an earlier period; in the lapse of centuries, it too, resigning its place, topples over headlong, an undermined mass; the surge dashes white and furious where the dense rock had rested before; and thus, in its slow but irresistible march, the sea gains upon the land. In the peculiar disposition and character of the prevailing strata of Orkney, as certainly as in the power of the tides which sweep athwart its coasts, and the wide extent of sea which, stretching around it, gives the waves scope to gather bulk and momentum, may be found the secret of the extraordinary height to which the surf sometimes rises against its walls of rock. During the fiercer tempests, masses of foam shoot upwards against the precipices, like inverted cataracts, fully two hundred feet over the ordinary tide-level, and, washing away the looser soil from their summits, leaves in its place patches of slaty gravel, resembling that of a common sea-beach. Rocks less perpendicular, how

ever great the violence of the wind and sea, would fail to project upwards bodies of surf to a height so extraordinary. But the low angle at which the strata lie, and the rectangularity maintained in relation to their line of bed by the fissures which traverse them, give to the Orkney precipices, remarkable for their perpendicularity and their mural aspect, exactly the angle against which the waves, as broken masses of foam, beat up to their greatest possible altitude. On a tract of iron-bound coast that skirts the entrance of the Cromarty Frith I have seen the surf rise, during violent gales from the north-west especially, against one rectangular rock, known as the White Rock, fully an hundred feet; while against scarcely any of the other precipices, more sloping, though equally exposed, did it rise more than half that height.

CHAPTER XIII.

Detached Fossils Remains of the Pterichthys - Terminal Bones of the Coccosteus, etc., preserved - Internal Skeleton of Coccosteus The shipwrecked Sailor in the Cave Bishop Grahame His Character, as drawn by Baillie His Successor Ruins of the Bishop's Country-house-Sub aërial Formation of Sandstone - Formation near New Kaye - Inference from such Formation Tour resumed Loch of Stennis Waters of the Loch fresh, brackish, and salt-Vegetation varied accordingly-Change produced in the Flounder by fresh water- The Standing Stones, second only to Stonehenge Their purpose - Their Appearance and Situation - Diameter of the Circle - What the Antiquaries say of it - Reference to it in the "Pirate " Dr. Hibbert's Account.

WE returned to Stromness along the edge of the cliffs gradually descending from higher to lower ranges of prepices, and ever and anon detecting ichthyolite beds in the weathered and partially decomposed strata. As the rock moulders into an incoherent clay, the fossils which it envelops become not unfrequently wholly detached from it, so that, on a smart blow dealt by the hammer, they leap out entire, resembling, from the degree of compression which they exhibit, those mimic fishes carved out of plates of ivory or of mother-of-pearl, which are used as counters in some of the games of China or the East Indies. The material of which they are composed, a brittle jet, though better suited than the stone to resist the disintegrating influences, is in most cases greatly too fragile for preservation. One may, however, acquire from the fragments a knowledge of certain minute points in the structure of the ancient animals to which they belonged, respecting which specimens of a more robust texture give no evidence. The plates of Coccosteus sometimes spring out as un

broken as when they covered the living animal, and, if the necessary skill be not wanting, may be set up in their original order. And I possess specimens of the head of Dipterus in which the nearly circular gill-covers may be examined on both surfaces, interior and exterior, and in which the cranial portion shows not only the enamelled plates of the frontal buckler, but also the strange mechanism of the palatal teeth, with the intervening cavities that had lodged both the brain and the occipital part of the spine. The fossils on the top of the cliffs here are chiefly Dipterians of the two closely allied genera, Diplopterus and Osteolepis.

A little farther on, I found, on a hill-side in which extensive slate-quarries had once been wrought, the remains of Pterichthys existing as mere patches, from which the color had been discharged, but in which the almost human-like outline of both body and arms were still distinctly traceable; and farther on still, where the steep wall of cliffs sinks into a line of grassy banks, I saw in yet another quarry, ichthyolites of all the three great ganoid families so characteristic of the Old Red, - Cephalaspians, Dipterians, and Acanthodians, ranged in the three-storied order to which I have already referred as so inexplicable. The specimens, however, though numerous, are not fine. They are resolved into a brittle bituminous coal, resembling hard pitch or black wax, which is always considerably less tenacious than the matrix in which they are inclosed; and so, when laid open by the hammer, they usually split through the middle of the plates and scales, instead of parting from the stone at their surfaces, and resemble, in consequence, those dark, shadow-like profiles taken in Indian ink by the limner, which exhibit a correct outline, but no details. We find, however, in some of the genera, portions of the animal preserved that are rarely