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appealed to the marine shells contained in the so-called raised sea-beach bed, to prove that a rise in the bed of the Forth has taken place within a comparatively recent geological period. In "The Lithology of Edinburgh," the instances adduced are proved to be unsatisfactory, and neither in accordance with the habits of the animals nor with the mode of distribution of the materials of a sea beach.

An attempt has lately been made to prove a rise of the coast of the Firth of Forth within the historical period, by an appeal to the so-called raised sea-beach bed deposits. It is contained in a communication by Mr Archibald Geikie, of the Geological Survey, and published in the "New Philosophical Journal" for July 1861. Mr Geikie states that he found "fragments of Roman pottery in a stratified deposit of marine silt, the deposition of which was going on during the Roman occupation of Britain." He says that "the strata with which this bed of silt is connected lie 25 feet above high-water mark, and are unequivocally those of the raised beach;" and therefore he infers that a rise in the land to this extent has taken place here since the time of the Romans.

In a communication to the Royal Society of Edinburgh by Mr A. Bryson, "On Hasty Generalisation in Geology," it was shown that this so-called marine silt-bed* (No. 5 of Mr Geikie's diagram), supposed to be of the Roman age, contained also abundance of broken pieces of recent pottery, fragments of bone belonging to the sheep and ox, and bits of burnt coal with vesicular cavities irregularly disseminated throughout the mass. This sand-pit is situated on the south side of the Junction Road at Leith, and at the foot of Bowling Green House garden. The section in this sand-pit furnishes a remarkable instance of old artificial deposits, bearing so close a resemblance to natural beds, that experienced observers, not geologically familiar with the locality, have entirely mistaken their nature and character. I examined this sand-pit upwards of two years ago, with the view of tracing the lateral extent inland of the marine deposits. The uppermost natural

*This bed is not distinctly stratified. There is no trace of lamination, and there are bits of burnt coal scattered throughout the mass.

deposit in the section consists of a bed of sandy clay, three or four feet thick, superimposed upon stratified beds of sand and gravel, and can be traced by its small columnar structure, due to shrinkage in drying and exposure, so characteristic of clays, as also by its light brown colour, onwards to the northern extremity of the section. This bed gradually blends with a dark unstratified mass of old humus, which, at the north end of the pit, is overlaid by a tongue of shot sand, with patches of humus intermixed, presenting an appearance of two beds. that are represented in Mr Geikie's diagram as beds 5 and 6. Bed No. 7, which Mr Geikie says "is the highest in the section, and consists of stratified sand and shingle, full of littoral shells, and some balani still attached," is not seen in the sand-pit section; and the only representative that has been observed is a narrow strip of marine shingle and sand, mixed with humus, laid down at the bottom of the garden. The whole of this locality is overspread with artificial deposits. A diagram, prepared by Mr Sharbau, assistant marine surveyor, gives a correct representation of the phenomena observed in this sand-pit section. The lowest bed consists of sand and coarse shingle, and contains abundance of worn marine shells, the balani adhering to the interior of the oyster valves. This bed is four or five feet above the sea level, and its character and contents are identical with a ripple-zone deposit. The overlying stratum is composed of marine sand, and varies in thickness. In this sand-pit it is five or six feet, whilst in an adjoining one, a few yards to the eastward, and now filled up, it was eleven feet thick, and contained abundance of worn marine shells and comminuted fragments. It is continuous with the bed of marine sand, in great part blown, on which the town of Leith is built, and is connected to the shore sand. This bed is frequently exposed in foundations for buildings and cuttings for drainage, and when passed through is found to rest on the boulder clay. The deposit of sand and gravel. which overlies this bed in the sand-pit section is destitute of marine remains, and appears to be of fluviatile origin. It is remarkably irregular, and rises at the south end of the sandpit into a protuberance six feet thick. The bed of marine sand disappears in the direction of the river, and the gravel

is cut off to the eastward, where the overlying bed of sandy clay, and the lower bed of marine sand are observed to come in contact. This protuberance of sand and gravel extends towards the centre of the sand-pit, where a depression occurs which has been filled up with humus. This short lateral ridge of sand and gravel presents an appearance similar to what is formed by the bifurcation of rivers, or by currents heaping up deposits along their margins. The uppermost bed of sandy clay, which forms part of the so-called stratified marine silt, has all the characters of a marsh silt or lacustrine deposit; and the neighbouring hollow indicates the existence. of a former lake. This is still a marsh, over which the Water of Leith occasionally flows as far as the Bonnington road; although the river is now confined within narrower limits, and guided by piers across the extensive foreshore of flat sand to its junction with the sea.

IV. On the Danger of Hasty Generalization in Geology; with Special Reference to the so-called Raised Sea-Beach at Leith. By ALEXANDER BRYSON, Esq., F.R.S.E.

As my friend Dr M'Bain was to favour us with a communication on this subject this evening, I thought it might interest the Society to add, as a sequel to his observations, a few notes, some of which were formerly brought by me before the Royal Society here.

It is proper, before alluding to the failings of our friends. in making hasty generalizations, to confess our own failures, so that by plucking out the beams from our own we more readily detect the motes in our neighbours' eyes. The first instance which I shall notice of erroneous conclusions, drawn from scanty data, occurred to myself in 1856. Our late lamented fellow, Dr Fleming, brought me one day a very beautiful specimen of Carrara marble, on which was exhibited the most decided marks of a fossil plant, and, being much engaged at that time in the microscopic study of the Carboniferous flora, I felt no hesitation in pronouncing it to be a true Stigmaria. This being a new fact in geology, of course the specimen was often exhibited to demonstrate the existence of

carboniferous fossils in the primitive limestone. Fortunately for truth, a friend obtained many similar specimens in the establishment of a marble-cutter in Leith Walk, where I soon found the true explanation of the structure which had led me to maintain its organic origin.

It is usual for the marble-cutters at Carrara, before sending out the blocks from the quarry, to reduce them into as small dimensions as possible. This operation is performed by what is called a matting-hammer, consisting of many separate and blunt teeth placed alternate to each other, and is used by bringing the hammer down, in a perpendicular direction, to the flat face of the marble block. By this method a series of quinquncial indentations are produced precisely similar to those found in Stigmaria, and, to render the illusion more perfect, where the percussion of the teeth of the hammer is greatest (which is at the point), the limestone at the bottom of each depression is more crushed, and being deprived of its air by the greater force, exhibits a different structure from the surrounding walls, and thus presents the regularity, both in shape and direction, of the protruding petioles of Stigmaria.

Unfortunately, before this discovery was made, my dear friend Professor Fleming died, and I have no doubt that this specimen is now lying in his cabinet, labelled on my authority as a Stigmaria. Another instance of the danger of hasty generalization which occurred to myself-the supposed native lead of Inch Mickery-was formerly brought before this Society, and is published in our Proceedings, vol. ii. p. 85.

I have now to deal with another instance in which a hasty generalization has met with more attention in the geological world than any of those I have mentioned, but not less than it deserved. Mr Geikie, in a paper published in the "Edinburgh Philosophical Journal," vol. xvi. p. 102, has stated his belief that the ground on which Leith is situated has risen to the extent of 25 feet since the Roman period. The section from which he has come to this conclusion is in a sand-pit at the Junction Road, Leith, and is represented in the diagram, which is the same as Mr Geikie used to illustrate his paper. He thus describes the succession of the strata as seen in the sand-pit:"The lowest bed (1) visible is one of coarse gravel or

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shingle, the pebbles being all well rounded, and loosely cemented in a sandy and somewhat ferruginous matrix. (2) Is a bed of fine white sand, about six feet thick. It is full of false bedding, the diagonal stratification being beautifully exhibited by the alternations of darker and lighter coloured layers. Its upper surface is irregular, and is overlaid by a well-marked seam (3) of sand and gravel, which averages about sixteen inches in thickness. Its lower part is gravelly and ferruginous. This stratum is covered by three or four inches of a stiff greenish clay (4), which contains numerous perpendicular (sometimes dichotomous) ferruginous pipes, probably marking the remains of the stems of plants. This stratum passes up into a bed (5), about six feet thick, of dark silt or sandy clay well stratified, having thin lenticular interlaminations of sand, with occasional oyster-valves, a few

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Section of Sand-pit, Junction Road, Leith.

stones, and fragments of bones and pottery. The upper part of this bed becomes more sandy, and graduates into the superincumbent stratum of brown sand (6). The highest bed of the section (7) consists of stratified sand and shingle full of littoral shells, and some of the stones having balani still attached. The irregular deposit (marked h in the diagram), which rests unconformably upon the edges of the strata just described, is a mass of loose humus, which has been thrown down here at no distant date, perhaps to fill up an irregularity of the surface. It is full of stones, bricks, bones, pieces of

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