[Footnote 63: _Quart. Jour. Geol. Soc._ vol. vi. pp. 120, 130. The cut given above (Fig. 33) is taken from one of these sections as modified by the late Sir Henry de la Beche (_Geological Observer_, p. 582). In the original the beds are inclined at a considerable angle, but for the sake of clearness they are here reduced to horizontality.] Applying, then, this deduction to the strata occurring on the horizon of the mountain limestone in Mid-Lothian, we are led to believe that the North Greens coal-seam marks the site of a former land-surface. It shows no vertical stems, but has all the other accompaniments of an ordinary seam, such as the underlying fire-clay and shale, with their included stigmariæ. And this conclusion has more than ordinary interest, for if it be true, we have evidence of a terrestrial formation among strata unequivocally marine; in other words, we see proofs either of an elevation or a filling-up[64] of the sea-bottom carried slowly on until land-plants grew up in matted swamps where once there swarmed corals and encrinites, and then of a gradual subsidence, so that marine organisms flourished again in abundance over the site of the submerged vegetation. It is not insisted that each of the thin coal-seams among the limestone strata marks a former terrestrial area. Some of them may possibly have resulted from the transport and deposition of plants borne from the land. Yet there are others of wide extent resting upon beds of fire-clay which contains stigmaria rootlets, &c. These I cannot but regard as the remains of plants that grew upon the spot. And so, while we recognise in the beds of limestone undoubted evidence of a former sea-bottom, I am persuaded we must equally admit that at least several of the coal-seams bear fair evidence of a former land-surface, scarcely raised above the sea-level indeed, but nourishing nevertheless a thickly matted vegetation. In this way we shall see the mountain limestone series of the Lothians to be not a purely marine formation, but one partly marine and partly deltoid, showing in the succession of its strata proofs of a gradual submergence, interrupted by movements of elevation, so that the area which at one period formed the ocean-bed became at a later time low delta-land, and after continuing perhaps for ages to stretch out its verdant surface beneath the open sky, sank again amid the corals of a wide-spread sea.