The geology of the neighbourhood of Edinburgh : (map 32) / by H.H. Howell and Archibald Geikie ; appendix and lists of fossils by J.W. Salter.

Date:
1861
Catalogue details

Licence: Public Domain Mark

Credit: The geology of the neighbourhood of Edinburgh : (map 32) / by H.H. Howell and Archibald Geikie ; appendix and lists of fossils by J.W. Salter. Source: Wellcome Collection.

Provider: This material has been provided by the Royal College of Physicians of Edinburgh. The original may be consulted at the Royal College of Physicians of Edinburgh.

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    is the only one in the district which seems, in a general way, to piece on to the section at Craigmillar. The sandstones and greenisli sandy shales there visible have long been well known to geologists. Their dip is easterly, and in a series of deep drains cut a few years ago along the street leading from the Castle to Arthur's Seat, the series of sandstones and reddish and greenish sliales was found to continue down to near Holyrood, having the same g-eneral eastern inclination. Hence the Old Town of Edin- burtrli stands on a series of Lower Carboniferous Sandstones and marly shales, of which the lowest visible portion occurs at the Castle and the highest at Salisbury Craig and Arthur's Seat. The strata at Salisbury Craig clearly indicate a higher strati- graphical position than those at Craigmillar. The green and reddish hue in the sandstones still remains, but the beds are thinner, more sparingly conglomeritic, and contain numerous thin alternations of green and red argillaceous shale, with some bands of coarse limestone. In the quarries above the greenstone of the Craig the sandstones are well exposed, many of their surfaces showing ripple-]narks along with the bores of annelids. On the east side of the Hunter's Bog these strata pass under the volcanic rocks of Arthur's Seat. Before entering upon the latter, however, it may be well to notice the development of the basement beds of the Lower Carboniferous group in other parts of the area embraced in the present Sheet. When the Lower Carboniferous rocks of Edinburghshire began to be formed the trappean ridge of the Pentlands had not wholl}- disappeared beneath the Old Red conglomerates and sandstones. Hence in several parts along the western flank of the hills, not- withstanding the long parallel faults, we find different horizons of the Lower Carboniferous series resting directly upon Upper Old Red felstones, and in other parts graduating downward into a diminished series of Upper Old Red conglomerates and sand- stones, which in like manner rest at different levels upon the felstones and on the underlying highly inclined Silurian strata. In the streams to the east and south of Warklaw Hill, a series of sandstones, shales, and thin limestones occurs, which possibly represent the similar strata overlying the traps of the Calton Hill ; at least they appear to be higher than the sandstones and shales of Arthur's Seat. They rest directly upon the felstone of Warklaw Hill, and from the felspathic character of their lower beds appear to have been derived from the waste of that rock. The floor on which they were deposited must have been some- what uneven, for about midway up the burn that descends into Clubbidean Reservoir from the south, a mass of the same felstone protrudes from beneath the enveloping strata.* These shales and sandstones contain Spheno'pterisaffinis,GypTis (the Burdie House species), Spirorhis (two species), Myalina. Although probably much modifled by the effects of the adjacent fault, the valley of the Clubbidean Reservoir seems to have existed as a sheltered * S«e ante, fig. 3, p. 11.