markets of the neighbouring towns, and still the supply keeps up ample as at first. Now the tracts of sand which they inhabit, if not properly quicksands, are at least extremely loose, especially when covered by the tide; and though the creatures succeed, so long as they live, in maintaining their proper place in them within a few inches of the surface, no sooner do they die than the shells begin gradually to sink downwards through the unsolid mass, till, reaching, at the depth of about six feet, a firmer stratum, they there accumulate, and form a continuous bed. The work of accumulation has been going on for many centuries; generation after generation has been dying, to undergo this process of burial,-this process of subarenaceous deposition, if I may so speak; and there are places in the estuary in which the shelly stratum has risen to within a foot or two of the surface. It forms a sort of quarry of shells; and when, about thirty years ago, there was a lime-work established in the neighbourhood, many thousand cart-loads were dug out and burned into lime. I had frequent occasion, some five or six years since, to pass through the estuary at seasons when the mere amateur would have perhaps stayed at home. There runs through it a stream of fresh water, that drains the flat fields and scattered lochans of Easter Ross; and on one of my winter journeys, after a sudden thaw, accompanied by heavy rains, I found the stream swollen to the size of a considerable river, and its bed excavated beneath the usual level some three or four feet, with the sectional line of sand and shells through which it had cut standing up over it like a wall. There was first, reckoning downwards, from a foot to eighteen inches of pure sand; and next, from two feet to two feet and a half of dead shells. The sandy tract all around, for many hundred acres in extent, used to be partially covered with water; every furrow of the ripples, and every depression of the surface, borrowed its full from the receding tide, and,

But on

from the general flatness, retained it till its return. this occasion, the surface-water had found an unwonted drainage, through the upright sectional front, into the newly excavated bed of the stream. It sank through the upper

arenaceous layer as through a filtering stone, and then came rushing through the stratum of shells underneath, brown with the sand which it swept from their interstices. Nor could there be a completer sifting process. For yards and roods together the shells were as thoroughly divested of the sandy matrix in which they had lain as if they had been carefully washed in a sieve. I was bold enough to infer from the phenomenon at the time, that the problem of the unmixed accumulations of shells may be, in at least some cases, not so difficult of solution as has been hitherto supposed. One has but to take for granted conditions such as those of the estuary of Nigg,—the incoherent bed, half a quicksand, and the subarenaceous deposition,-to account for their original production, and the superadded conditions of the surface-water and the free drainage, to account for their after clearance of extraneous matter.

CAUTION TO GEOLOGISTS ON THE FINDING OF REMAINS.

IN consolidated slopes it is not unusual to find remains, animal and vegetable, of no very remote antiquity. I have seen a human skull dug out of the reclining base of a clay bank, once a precipice, fully six feet from under the surface. It might have been deemed, not without a degree of plausibility, the skull of some long-lived contemporary of Enoch, -perchance that of one of the accursed race,—

'Who sinned and died before the avenging flood.'

Nay, a fine theory was in the act of being formed regarding it, which affected the whole deposit; but, alas! the labourer dug a little further, and struck his pickaxe against an old

Gothic rybat, that lay deeper still. There could be no mistaking the character of the chamfered edge that still bore the marks of the tool, nor that of the square perforation for the lock-bolt; and the rising theory straightway stumbled against it and fell. Both rybat and skull had come from an ancient burying-ground, situated on a projecting angle of the table, and above.

REMARKS ON UNDERLYING CLAY ON LEVEL MOORS.

ON level moors, where the rain-water stagnates in pools, and a thin layer of mossy soil produces a scanty covering of heath, we find the underlying clay streaked and spotted with patches of white. As in the spots and streaks of the Red Sandstone formations, Old and New, the colouring matter has been discharged without any accompanying change having taken place in the mechanical structure of the substance which it pervaded; for we find the same mixture of arenaceous and aluminous particles in the white as in the red portions. And the stagnant water above, acidulated, perhaps, by its various vegetable solutions, seems to have been in some way connected with these appearances. In almost every case in which a crack through the clay gives access to the oozing moisture, we find the sides bleached, for several feet downwards, to nearly the colour of pipe-clay; we find the surface, too, when divested of the soil, presenting for yards together the appearance of sheets of half-bleached linen. Now, the peculiar chemistry through which these changes are effected might be found to throw much light on similar phenomena in the older formations. There are quarries in the New Red Sandstone in which almost every mass of stone presents a different shade of colour from that of its neighbouring mass, and quarries in the Old Red, whose strata we find streaked and spotted

like pieces of calico. And their variegated aspect seems to have been communicated in every instance, not during deposition, nor after they had been hardened into stone, but when, like the boulder-clay, they had existed in an intermediate state.

TRAVELLED BOULDERS NOT ASSOCIATED WITH CLAY.

ALL the travelled boulders of the north do not seem associated with the clay: we find them occurring, in some instances, in an overlying gravel, and in some instances resting at high levels on the bare rock. I have seen, on the hill of Fyrish,-a lofty eminence of the Lower Old Red which overlooks the upper part of the Cromarty Firth,-a boulder of an exceedingly beautiful, sparkling hornblende, reposing on a stratum of yellow sandstone, fully a thousand feet over the sea, where there is not a particle of the clay in sight. We find these travellers furnishing specimens of almost all the primary rocks of the country,-its gneisses, schistose and granitic, its granites, red, white, and grey, its hornblendic and micaceous schists, and occasionally, though more rarely, its traps. The stone most abundant among them, and which is found occurring in the largest masses, is a well-marked granitic gneiss, in which the quartz is white, and the feldspar of a pink colour, and in which the mica, intensely black, exists in oblong accumulations, ranged along the line of stratification in interrupted layers. No rock of the same kind is to be found in situ nearer than thirty miles. We find granitic boulders of vast size abundant in the neighbourhood of Tain, especially where the coach-road passes towards the west through a piece of barren moor, and on the range of sea-beach below. One enormous block, of a form somewhat approaching the cubical, is large enough, and seems solid enough, to admit

of being hewn into the pedestal of some colossal statue; but instead of being thus appropriated to form part of a monument, it has lately been converted of itself into a whole monument. When I last passed the way, I found it dedicated, in an inscription of nine-inch letters, 'to the memory of the immortal Scott.' Nature had dedicated it to the memory of one of her great revolutions ages before; but since the dedicator had determined on adding, in Highland fashion, a stone to the cairn of Sir Walter, it would certainly have been no easy matter to have added to it a nobler one.

GRANITIC GNEISS AND SANDSTONE, WITH THE CONDITIONS OF

THEIR UPHEAVAL.

ON entering on the granitic rock, we find the strata, strangely disturbed and contorted, lying, in the course of a few yards, in almost every angle, and dipping in almost every direction. And not only must there have been a complexity of character in the disturbing forces, but the rock on which they acted must have been singularly sus ceptible of being disturbed. The strata of the sandstone were, at the period of their upheaval, the same brittle, rigid plates of solid stone that they are now. The strata of the granitic gneiss were characterized, on the contrary, during their earlier periods of disturbance, by a yielding flexibility: they were capable of being bent into sharp angles without breaking. We see them running in zig-zag lines along the precipices, now striking downwards, now ascending upwards, now curved like a relaxed Indian bow in one direction, now curved in a contrary one, like the same bow when fully bent. The strata of the sandstone, like a pile of glass-panes laid parallel, existed in a state in which they could be either raised in any given angle, or, if the acting forces were vio