is contemporaneous with the mass now under notice. There are, indeed, strong grounds for believing that boulder-clays may be of different ages, and even generated under considerably different conditions. Hence the great value of a rigid examination of the phenomena, in this district, as a type or standard, wherewith the occurrences of other districts may be compared. When the resemblances and the differences shall have been carefully determined, our generalisations may then be expressed with greater confidence. Meanwhile it is of importance to secure accurate observations respecting the character of the surfaces of the rocks on which the deposit rests, the character of the materials, and the evidence of intermittency exhibited in its upper members.

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CHAPTER VI.

Akumite series-Silt-Drift-peat, Sand, and Gravel-Organic Remains of Plants and Animals-Chalk Flints-Marine or Lacustrine Origin-Sand Hills-Erratics.

THE group of beds in the ascending series, now demanding consideration, will usually be found included under the term Alluvium. This name, however, is usually attached to the ordinary deposit in lakes and estuaries, or on the margins of rivers, and hence, if employed, would be too vague or indefinite. The phrase Brick-clay Beds would in many cases be appropriate; but many other beds belonging to older strata, such as the argillite of the coal-measures in the neighbourhood, are likewise extensively used for the purposes of the potter.

The group consists of three members, silt, sand, and gravel, varying considerably in character in the different localities. The examples are numerous, of easy access, and well exposed.

1. Silt. This seems, in all the localities which have occurred for examination, to be the lowest or basement bed. It rests on the boulder-clay, where it is compact, and not on the upper or arenaceous portions of the mass. The surface of the boulder-clay, when fairly exposed, is uneven, with projecting but fixed boulders. Occasionally detached ones occur, resting on the surface, and surrounded on the sides and top by the silt. The evidence is indeed very plain that, subsequent to the deposition of the Taragmitic series, and previous to the commencement of the Akumite group, extensive denudations had taken place, by which the newer or upper portion of the former had been removed.

One of the most interesting examples of silt may be observed in the neighbourhood of Granton, on the terrace to the

south of the harbour, and overhanging the village. The base of the bed, or the surface of the boulder-clay, may be about twenty feet above high-water mark. It is moderately even, and seems to have been a flat margin projecting from the terrace on the south, to which it is continuous by a gentle curvature. The bed at its northern or free edge is five or six feet deep, varying, however, considerably in the different portions which have been exposed. It thins off towards its south edge, where it joins the higher terrace on the north margin of the Golden Acre flat. At its junction with this last terrace, and where it thins off, there is no trace of ripple action, or margin of shingle, to indicate a sea-beach. The silt itself is of the same blackish hue as the boulder-clay, of which it appears to have been the finer portions washed out. The probability of this origin may be strengthened by washing out the finer part of the boulderclay, and allowing the fine mud thus obtained to subside. The product will be a clay differing in no respect from the silt. The boulder-clay has a colour peculiar to the locality, being blackish in the coal districts, and reddish in the region of the old red sandstone, and the silt beds resting on it exhibit corresponding colours. The Eden in Fife is the colour boundary of the two series to the north.

The bed of silt is uniform throughout, and gives no indication of the carrying power with its suspended materials, having been subject to any intermittency. Even when the clay has been exposed for some time to the weather, the traces of stratification are extremely imperfect, a character almost peculiar to this bed. Its upper surface, however, immediately passes into a bed of coarse sand or gravel of a somewhat uniform character, with here and there films of finer materials, indicating a horizontal stratification, or rather a dip northward of four or five degrees. This bed of gravel, like the inferior silt, also abuts against the diluvial terrace, which forms the southern boundary of this silt basin.

No organic remains, as far as we have seen or heard of, have been discovered in the various portions of the clay which have been removed, or in its cover of gravel. Here, then, with

out determining whether this silt has been formed in an estuary or a lake, undoubted proof that water standing over this shelf of diluvium, and in comparative stillness, permitted the mud introduced to subside to the thickness referred to, continuously, that is without any obvious films of sand indicating intermittency, occasional freshets, or tides. The bed of silt, on its northern margin, seems to have been subjected to a washing or scooping out of its substance by ripple action, for the gravel has been observed to overlap the extremity of the upper portion of the silt, and to fill up some of the excavations. (See Fig. 5.)

The soil over the gravel bed, constituting the covering of the silt, is nearly horizontal, and seems to indicate its having been assorted by gravity in rather shallow water.

In the plain immediately to the south of this deposit of silt, and about a quarter of a mile from the northern margin or terrace to which we have referred, there is a hollow, and in it another apparently extensive deposit of silt has been exposed for brick-making purposes. As in the former example, the silt here rests on the uneven surface of the boulder-clay, without the intervention of gravel or shingle, and this floor is of a uniform compactness, resembling the inferior part of the diluvial bed. The silt here is more distinctly laminated, and it passes by alternations into sand at its upper part, with occasionally portions of gravel. The soil itself has been formed from a bed two or three feet in thickness of unlaminated tough

light-coloured clay, into which the upper sand-beds imperceptibly pass. No organic remains have been detected in this deposit as far as known to us.

In looking at the sections from time to time displayed on the cliff between Granton and Newhaven, it appears that while the silt invariably reposes on the boulder-clay as its floor, it graduates above into various alternations of silt, sand, and gravel. To the south of our second example, and nearly at the same level, another deposit of silt was exposed a few years ago, and has been described by Mr Milne Home, in his valuable paper on the "Parallel Roads of Lochaber," p. 50:

"When the Edinburgh and Newhaven Railway was being constructed, there was found on the turnpike-road lying between Leith and Golden Acre, an extensive bed of sand about ten feet thick, below it a bed of peat one foot thick, below it a bed of laminated blue clay about ten feet thick, and below it the well-known boulder-clay. The bed of peat contained roots of trees, which evidently had grown in the clay, as their roots were found passing through the peat into the clay. These roots belonged apparently to the hazel; but the only parts undecayed were the bark. In this peat-bed there were stems of reeds and other marsh plants, and numbers of small seeds of some shrub, not unlike those of a species of whin. These seeds, Mr M'Nab of the Experimental Gardens attempted to germinate, but without success. There was also some elytra of beetles. This bed of peat is from 70 to 80 feet above the I traced it for at least 100 yards along the cut of the railway, in a north and south direction. How much it extends in an east and west direction, I had no means of ascertaining. But it certainly extends to the westward for at least a mile.* Over this bed of peat, there is, as already mentioned,

sea.

"The late Captain Boswell of Wardie shewed to me a statement of the strata gone through in sinking two coal-pits on his property, which adjoins the locality alluded to in the text. At Pit No.1, which was 71 feet above the sea, a bed of sand 9 feet thick was first gone through, below which there was 15 feet of clay, first soft, and then hard and stony. At Pit No. 2 (250 yards to the west of Pit No. 1), the first bed gone through was 9 feet of 'sand and soft clay,' below which was 21 feet of stony and black clay.'"