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HASWELL—ON THE DENUDATION OE ABTUTJIt's SEAT. 93 lines of growth. In a young state the shell is longitudinally ribbed, the ribs being tumid and close together; no trace of this is seen iu the adult. A second specimen, probably of the same species, is rather larger, and has a rib between the suture and the marginal angle, and six primary ribs on the body-whorl. Both these examples are distorted by pressure. The smaller ex­ ample (figured) is compressed laterally. The rock is a very hard chalk, much resembling some of the lighter-coloured clay concretions; fossils are yellowish. (?) FTJSD-S. This form diners from the Brighton specimens chiefly in the large number of equal- sized ribs, a character to which little importance can be given; it may be varietal, but more probably is but an adult ornament, just as are the longitudinal ribs, a feature pecu­ liar to the young. The lip is a little inflected. The space between the posterior two ribs appears to have supported a sharp projecting keel, now broken away. SOLAHITTM BlNGHAMI (Baity). Shell thick, much depressed, not half so high as wide; composed of about six whorls, which very gradually increase in size. The upper side of the shell is a greatly depressed cone; the under side a large conical hollow. The whorls are five-angular; they are attached by one side, two converge interiorly to form the base, one perpendicular forms the side of the shell, and the fifth forms the slightly oblique upper surface. This last form of the upper surface of the whorl is ornamented mar­ ginally by upwards of forty tubercles, which are elongated in a direction at right angles with the line of growth. A second row, more numerous and much smaller, passes round near to the suture. Both the interspace and tubercles are finely striated spirally. The perpendicular side is not more than half the width of the outer basal space; it has on its lower margin a row of tubercles similar to that on its upper margin, but they are narrower and half as numerous again. The tubercles so entirely occupy the side that the groove between the two rows is not half so wide as either of them. The outer part of the base is very finely cancellated; the angle it makes with the inner half is nodulated with seventeen large tubercles. The inferior suture is much more impressed than the superior one, and the sutural margin of the base is ornamented with a row of tubercles, about as numerous as that on the upper margin of the side. The umbilicus is nearly as deep as wide. ON THE DENUDATION OP AKTHUE'S SEAT. Br JAMES HASWELI., M.A. " Quid magis est saxo durum ? quid mollius unda ? Dura tamen molli saxa cavantur aqua." The condition of Central Scotland during the long period repre- 94 THE GEOLOGIST. sented by the Secondary formations is involved in darkness. On the east and west coasts of Scotland rocks of Secondary age occur north of the Grampians, but of the physical history of Central Scotland during the time these rocks were deposited, we know nothing. From the time of the deposition of our Upper Coal-beds, or, it may be, of some Permian Sandstones, up till the time when the whole island was locked fast in one immense mantle of ice, we are almost entirely ignorant of what was going on in that part of the country which lies between the Grampians and the Forth. And the man who shall de­ cipher for us the physical geography of that period, and reveal to us the old surface of that district, with its vegetation and animal pro­ ductions, prior to the time of the Boulder Clay, will have rendered no small service to the cause of Scottish geology. But although we have not as yet been able to trace the old surface of the land, we are not altogether without data to guide us in our researches. One thing is clear and certain,—a great change was taking place over the whole face of this region. Both during and after the deposition of the coal-measures, great volcanic agencies were at work. In the neighbourhood of Edinburgh they were particularly active. They had been so during the Old Red Sandstone period, and contributed in no small degree to the forma­ tion of the Pentland Hills. But towards the close of the Old Bed period and the commencement of that time when our Lower Carbo­ niferous Sandstones were being formed, the Pentland ridge began to sink under those Carboniferous seas. The crater of eruption, which had been so active in the Pentland area, and produced that varied mass of material now presented to us as sheets of felstone and ashy \ bands, became gradually quiescent, till at last it was entirely covered \ over with the increasing deposits. But, while these deposits were j being accumulated, the igneous forces broke out again at Arthur's J Seat. Most of the rocks which now form the eastern part of the hill belong to this period. The greenstone of the Long Row, the red nodular ash and the thin bands of red ashy sandstone to be seen in a section at the south side of the Queen's Drive, the green felspathic ash of the Dry Dam, the black columnar basalt above it (which also constitutes the crag on which stands St. Anthony's Chapel), the two basalts behind St. Anthony's, and which* form the lower part of Dunsapie Hill and Calton Hill, and lastly, that group of felstones \ which form the remainder of the eastern part of the hill from the top of Dunsapie across Whinny Hill to St. Margaret's Station, and which make up most of the Calton Hill,—all these igneous productions were contemporaneous with the Lower Carboniferous strata, and are found/interbedded with them. Consequently, all these traps are subaqueous. Layers of sediment were first formed, then an eruption of lava took place, which spread itself in sheets over the strata; then more layers of mud and sand were deposited by the ocean, and •. then more sheets of lava ejected by the igneous agency below. It ; is evident, moreover, that these traps must have been more or less ; horizontal, for if they had been poured over an inclined surface, ; J HASWELL—OK THE DENUDATION OF AETHUil's SEAT. 95 they would have collected in masses at the foot of the declivity,—a state in which we do not now fiud them. THE LOWER CARBONIFEROUS STRATA AND INTERBEDDED TRAPS 01 ARTHUR'S SEAT, IN THEIR ORIGINAL POSITION. Kg. 1. A Mass of overlying Carboniferous Sandstones, Limestones, Shales, etc. A group of Felstones. Three Basalts above Ash of Dry Dam. Ash of Dry Dam. Ashy Sandstones, Shales, and Limestones. Greenstone of the Long Row. Sandstones, ^^^ Shales, and fine ; Conglomerates. The Beds indicated by thin lines are Carboniferous strata; those by thick lines are Tnterbedded Traps. In this way the elevating processes continued their unceasing work, stratum after stratum was deposited, sheet after sheet of lava ejected and consolidated, until, when the last of the porphyritic felstones had been produced, the igneous centre gave signs of cooling, and all became comparatively quiet. Then the sediment of these Lower Carboniferous seas accumulated over the solidified lavas, ganoid fishes revelled undisturbed in the Burdiehouse Estuary, and plants peculiar to the period were entombed in the mud; while, as the result of all, 96 THE GEOLOGIST. | after many ages had elapsed and hundreds of years had passed away, j an immense series of strata was elaborated, which extended continu- | ously over the site of the Pentlands. The same waters under which j was laid down the ash of the Dry Dam, and which held hi solution | the substances which fill the amygdaloidal cavities of the greenstones | and felstones above it, also deposited above these rocks an enormous j series of beds, 3000 ft. thick at least, of sandstone, shale, and lime- ,; stone, the edges of which are seen on the beach eastwards from i Portobello. and at East Cairn Hill on the Pentlands, at a height of i 1839 ft. above the level of the sea, i. e. 1000 ft. above Arthur's Seat. { These rocks also extend northwards into Fife. This is represented J in the accompanying diagram. j It is perfectly evident then, from what has been already said, that j Lower Carboniferous strata must have been elaborated far above the \ present altitude of Arthur's Seat, and that their area extended for a • considerable distance on all sides, overlying the whole ridge of the \ Pentlands. It is also pretty clear, both from the horizontal beds of j sandstone on the summit of East Cairn Hill, and from the state of the case generally, that these strata were at first laid down in a hori­ zontal position, or at all events very nearly so. < Now, the next stage through which these rocks passed is easily de­ termined. An upheaving movement must have taken place, by which the whole beds of the hill, already alluded to as forming the eastern part, on to the centre of the Musselburgh basin, were raised into the inclined position in which we now find them. If evidence of this up­ heaval is wanted, we have only to point to St. Leonard's Craig, Salis­ bury Craigs, with the two dykes cutting through them, and the Dasses, "< the only intrusive traps of the hill, and all found on the western side. \ The effects of this upheaval are well displayed at Salisbury Craigs, j where the beds have an easterly dip, being raised on the west and depressed on the east, and where both the sandstone and the green- j stone are altered in colour and texture at the point of contact.

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