children of the place, and are known among them as the giants' graves. They lie against the green bank, each from forty to sixty yards in length, and from six to ten yards in height, with their feet to the shore, and their heads on the top of the escarpment; and when the evening sun falls low, and the shadows lengthen, they form, from their alternate bars of light and shade, that remind one of the ebon and ivory buttresses of the poet, a singularly pleasing feature in the landscape. I have sometimes wished I could fix their features in a calotype, for the special benefit of my friends the landscape painters. This vignette, I would fain say, represents the boulder-clay after its precipitous banksworn down, by the frosts and rains of centuries, into parallel runnels, that gradually widened into these hollow grooves-had sunk into the angle of inclination at which the disintegrating agents ceased to operate, and the green sward covered all up. You must be studying these peculiarities of aspect more than ever you studied them before. There is a time coming when the connoisseur will as rigidly demand the specific character of the various geologic deposits in your rocks and scaurs, as he now demands specific character in your shrubs and trees.

I have said that the boulder-clay exhibits certain unique appearances, which connect its origin in the several localities with one set of causes, and which no other deposit presents. On examining the boulders which it encloses, we find them strongly scarred and scratched. In most instances, too, the rock on which the clay rests,-if it be a trap, or a limestone, or a finely-grained sandstone, or, in short, any rock on which a tool could act, and of a texture fitted to retain the mark of the tool,-we find similarly scarred, grooved, and scratched. In this part of the country the boulder-clay contains scarce any fossils, save fragments of the older organisms derived from the rocks beneath; but in both the north and south of Scotland,-in

Caithness, for instance, and in Wigtonshire,-it contains numerous shells, which, both in their species and their state of keeping, throw light on the origin of the formation. But of that more anon. Let me first remark, that the materials of the level marginal strip of ancient sea-beach beneath the old coast line seem, like the materials of the existing seabeach, to have been arranged wholly by the agency of water. But in the boulder-clay we find a class of appearances which mere water could not have produced. Not only are the larger pebbles and boulders of the deposit scratched and grooved, but also its smaller stones, of from a few pounds to but a few ounces, or even less than an ounce, in weight; and this, too, in a peculiar style and direction. When the stones are decidedly of an oblong or spindle shape, the scratchings occur, in at least four cases out of every five, in the line of their longer axis. Now, the agent which produced such effects could not have been simply water, whether impelled by currents or in waves. The blacksmith, let him use what strength of arm he may, cannot bring his file to bear upon a minute pin until he has first locked it fast in his vice; and then, though not before, his tool bears upon it, and scratches it as deeply as if it were a beam of iron of a ton weight. The smaller stones must have been fastened before they could have been scratched. Even, however, if the force of water could have scratched and furrowed them, it would not have scratched and furrowed them longitudinally, but across. Stones, when carried adown a stream by the torrent, or propelled upwards along a beach by the waves, present always their broader and longer surfaces; and the broader and longer these surfaces are, the further are the stones propelled. They are not launched forwards, as a sailor would say, end on, but tumbled forwards broadside. They come rolling down a river in flood, or upwards on the shore in a time of tempest, as a hogshead rolls down a declivity.

In the boulder-clay, on the contrary, most of the pebbles that bear the mark of their transport at all were not rolled, but slidden forward in the line of their longer axis. They were launched, as ships are launched, in the line of least resistance, or as an arrow or javelin is sent on its course through the air. Water could not have been the agent here, nor yet an eruption of mud propelled along the surface by some wave of translation produced by the sudden upheaval of the bottom of the sea, or by some great wave raised by an earthquake.

But if water or an eruption of mud could not have produced such effects as the longitudinal scratching, let us ask what could have produced them? There are various processes going on around us, by which the scratchings on the solid rocks beneath are occasionally simulated with a less or greater degree of exactness. In some of our shallow Highland fields, for instance, I have seen the rock beneath, or the stones buried at the depth of but a few inches from the surface, scarred by the plough with ruts not very unlike the larger ones on the stones and rocks of the boulder-clay; but in these plough-scarred surfaces the polish is wanting. Again, in some of our steeper lanes, if a fine-grained trap has been used in the pavement, we find that it soon polishes and wears down under the iron-armed feet of the passengers, and becomes scratched in the line of their tread, in a style not very distinguishable, save for the absence of the deeper furrows, from that of the scratched and polished rock-pavements of the boulder-clay. But I know of only one process by which, on a small scale, all the phenomena of the boulder-clay could be produced,-more especially, however, the phenomena of its oblong pebbles scratched in the lines. of their longer axis; and my recollection of that one dates a good many years back. When, more than a quarter of a century ago, the herring fishing began to be prosecuted with vigour in the north of Scotland, many of the Highland

woods of natural birch and alder were cut down for the manufacture of barrels, and floated in rafts along the rivers to the sea. And my opportunities of observing these rafts, as they shot along the more rapid reaches of our mountain streams, or swept over their shallower ledges, grazing the bottom as they passed, naturally led me to inquire into their operations upon the beds of the streams adown which they were floated. Let us advert to some of these. When a

large raft of wood, floated down a rapid river, grates heavily over some shallow bank of gravel and pebbles resting on the rock beneath, it communicates motion, not of the rolling but of the lurching character, to the flatter stones with which it comes in contact. It slides ponderously over them; and they with a speed diminished in ratio from that of the moving power in proportion to the degree of friction below or around, slide over the stones or rock immediately beneath. And thus, to borrow my terminology from our Scotch law courts, they are converted at once into scratchers and scratchees. They are scratched by the grating, sandarmed raft, which of course moves quicker than they move; and they scratch, in turn, the solid mass or embedded fragment along which they are launched. Further, if the gravelly shoals of the stream have, as is not uncommon in the shallows of our Highland rivers, their thickly-set patches of pearl mussels, many of these could scarce miss being crushed and broken; and we would find not a few of their fragments, if much subjected to the friction of the rafting process, rounded at their edges, and mayhap scratched and polished like the stones. Nor is it difficult to conceive of a yet further consequence of the process. A vast number of rafts dropping down some river from day to day and year to year, and always grating along the same ledges of sandstone, trap, or shale, would at length very considerably wear them down; and the materials of the waste, more or less argillaceous, according to the quality of the rock, would be depo

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sited by the current in the pools and gentler reaches of the stream below. Even the continual tread of human feet in a crowded thoroughfare soon wears down the trap or sandstone pavement, and converts the solid stone into impalpable mud. Further, the colour of the mud or clay would correspond, as in the thoroughfare or public road, with the colour of the rocks or stones which had been grooved down to form it; and there would occasionally mingle in the mass thus originated, rounded fragments of shells and pebbles scratched in the line of their longer axis.

Now, in the boulder-clay we find all these peculiarities remarkably exemplified. It contains, as has been shown, the oblong stones scratched longitudinally; we find it thickly charged in various parts of Scotland, though not in our own immediate neighbourhood, with worn and rounded fragments of broken shells; and we see it almost invariably borrowing its colour from the rocks on which it rests,--a consequence, apparently, of its being the dressings of these rocks. There is a peculiar kind of clay which forms on the surface of a hearthstone or piece of pavement, under the hands of a mason's labourer engaged in rubbing it smooth with water and a polisher of gritty sandstone. This clay varies in quality and colour with the character of the stone operated upon. A flag of Arbroath pavement yields a bluishcoloured clay; a flag of the Old Red of Ross or Forfarshire, a reddish coloured clay; a flag of Sutherlandshire Oolite, or of the Upper Old Red of Moray or of Fife, a pale yellowish clay. The polishing process is a process which produces clay out of stones as various in tint as the colouring of the various stones which yield it; and in almost every instance does the clay thus formed resemble some known variety of the boulder-clay. The boulder-clay, in the great majority of cases, is, both in colour and quality, just such a clay as might be produced by this recipe of the mason's labourer from the rocks on which it rests. The red sandstone rocks