article the authorship of which will scarcely be mistaken. "We have here," says the writer, after first describing the sounds of Jabel Nakous, and then referring to those of Eigg, "the phenomenon in its simple state, disembarrassed from reflecting rocks, from a hard bed beneath, and from cracks and cavities that might be supposed to admit the sand; and indicating as its cause, either the accumulated vibration of the air when struck by the driven sand, or the accumulated sounds occasioned by the mutual impact of the particles of sand against each other. If a musket-ball passing through the air emits a whistling note, each individual particle of sand must do the same, however faint be the note which it yields; and the accumulation of these infinitesimal vibrations must constitute an audible sound, varying with the number and velocity of moving particles. In like manner, if two plates of silex or quartz, which are but large crystals of sand, give out a musical sound when mutually struck, the impact or collision of two minute crystals or particles of sand must do the same, in however inferior a degree; and the union of all these sounds, though singly imperceptible, may constitute the musical notes of the Bell Mountain, or the lesser sounds of the trodden sea-beach at Eigg."

Here is a vigorous effort made to unlock the difficulty. I should, however, have mentioned to the philosophic writer,

what I inadvertently failed to do, that the sounds elicited from the sand of Eigg seem as directly evoked by the slant blow dealt it by the foot, as the sounds similarly evoked from a highly waxed floor, or a board strewed over with ground rosin. The sharp shrill note follows the stroke, altogether independently of the grains driven into the air. My omission may serve to show how much safer it is for those minds of the observant order, that serve as hands and eyes to the reflective ones, to prefer incurring the risk of

being even tediously minute in their descriptions, to the danger of being inadequately brief in them. But, alas! for purposes of exact science, rarely are verbal descriptions otherwise than inadequate. Let us look, for example, at the various accounts given us of Jabel Nakous. There are strange sounds heard proceeding from a hill in Arabia, and various travellers set themselves to describe them. The tones are those of the convent Nakous, says the wild Arab; there must be a convent buried under the hill. More like the sounds of a humming-top, remarks a phlegmatic German traveller. Not quite like them, says an English. one in an Oxford gown;- they resemble rather the striking of a clock. Nay, listen just a little longer and more carefully, says a second Englishman, with epaulettes on his shoulder: "the sounds at their commencement may be compared to the faint strains of an Eolian harp when its strings first catch the breeze," but anon, as the agitation of the sand increases, they "more nearly resemble those produced by drawing the moistened fingers over glass." Not at all, exclaims the warlike Zahor Ed-din Muhammed Baber, twirling his whiskers: "I know a similar hill in the country towards Hindu-kush: it is the sound of drums and nagarets that issues from the sand.” All we really know of this often-described music of the desert, after reading all the descriptions, is, that its tones bear certain analogies to certain other tones,-analogies that seem stronger in one direction to one ear, and stronger in another direction to an ear differently constituted, but which do not exactly resemble any other sounds in nature. other sounds in nature. The strange music of Jabel Nakous, as a combination of tones, is essentially unique.

CHAPTER V.

Trap-Dykes" Cotton Apples"— Alternation of Lacustrine with Marine Remains - Analogy from the Beds of Esk - Aspect of the Island on its narrow Front — The Puffin - Ru-Stoir- Development of Old Red Sandstone - Striking Columnar character of Ru-Stoir - Discovery of Reptilian Remains-John Stewart's wonder at the Bones in the Stones-Description of the Bones "Dragons, Gorgons, and Chimeras"— Exploration and Discovery pursued The Midway Shieling - A Celtic Welcome-Return to the Yacht-"Array of Fossils new to Scotch Geology "-A Geologist's Toast - Hoffman and his Fossil.

WE leave behind us the musical sand, and reach the point of the promontory which forms the northern extremity of the Bay of Laig. Wherever the beach has been swept bare, we see it floored with trap-dykes worn down to the level, but in most places accumulations of huge blocks of various composition cover it up, concealing the nature of the rock beneath. The long semicircular wall of precipice which, sweeping inwards at the bottom of the bay, leaves to the inhabitants between its base and the beach their fertile meniscus of land, here abuts upon the coast. We see its dark forehead many hundred feet overhead, and the grassy platform beneath, now narrowed to a mere talus, sweeping upwards to its base from the shore,- steep, broken, lined thick with horizontal pathways, mottled over with ponderous masses of rock.

Among the blocks that load the beach, and render our onward progress difficult and laborious, we detect occasional fragments of an amygdaloidal basalt, charged with a white zeolite, consisting of crystals so extremely slender that the balls, with their light fibrous contents, remind us of cotton

apples divested of the seeds. There occur, though more rarely, masses of a hard white sandstone, abounding in vegetable impressions, which, from their sculptured markings, recalled to memory the Sigillaria of the Coal Measures. Here and there, too, we find fragments of a calcareous stone, so largely charged with compressed shells, chiefly bivalves, that it may be regarded as a shell breccia. There occur, besides, slabs of fibrous limestone, exactly resembling the limestone of the ichthyolite beds of the Lower Old Red; and blocks of a hard gray stone, of silky lustre in the fresh fracture, thickly speckled with carbonaceous markings. These fragmentary masses, all of them, at least, except the fibrous limestone, which occurs in mere planklike bands, represent distinct beds, of which this part of the island is composed, and which present their edges, like courses of ashlar in a building, in the splendid section that stretches from the tall brow of the precipice to the beach; though in the slopes of the talus, where the lower beds ́appear in but occasional protrusions and landslips, we find some difficulty in tracing their order of succession.

Near the base of the slope, where the soil has been undermined and the rock laid bare by the waves, there occur beds of a bituminous black shale, resembling the dark shales so common in the Coal Measures, that seem to be of fresh water or estuary origin. Their fossils, though numerous, are ill preserved; but we detect in them scales and plates of fishes, at least two species of minute bivalves, one of which very much resembles a Cyclas; and in some of the fragments, shells of Cypris lie embedded in considerable abundance. After all that has been said and written by way of accounting for those alternations of lacustrine with marine remains, which are of such frequent occurrence in the various formations, secondary and tertiary, from the Coal Measures downwards, it does seem strange enough

that the estuary, or fresh-water lake, should so often in the old geologic periods have changed places with the sea. It is comparatively easy to conceive that the inner Hebrides should have once existed as a broad ocean sound, bounded on one or either side by Oölitic islands, from which streams descended, sweeping with them, to the marine depths, productions, animal and vegetable, of the land. But it is less. easy to conceive, that in that sound, the area covered by the ocean one year should have been covered by a freshwater lake in perhaps the next, and then by the ocean again a few years after. And yet among the Oölitic deposits of the Hebrides evidence seems to exist that changes of this nature actually took place. I am not inclined to found much on the apparently fresh-water character of the bituminous shales of Eigg;-the embedded fossils are all too obscure to be admitted in evidence; but there can exist no doubt that fresh water, or at least estuary formations, do occur among the marine Oölites of the Hebrides. Sir R. Murchison, one of the most cautious, as he is certainly one of the most distinguished, of living geologists, found in a northern district of Skye, in 1826, a deposit containing Cyclas, Paludjna, Neritina, all shells of unequivocally fresh-water origin,— which must have been formed, he concludes, in either a lake or estuary. What had been sea at one period had been estuary or lake at another. In every case, however, in which these intercalated deposits are restricted to single strata of no great thickness, it is perhaps safer to refer their formation to the agency of temporary land-floods, than to that of violent changes of level, now elevating and now depressing the surface. There occur, for instance, among the marine Oölites of Brora,the discovery of Mr. Robertson, of Inverugie, two strata containing fresh-water fossils in abundance; but the one stratum is little more than an inch in thickness, the other