[276] Geol. Mag., vol. vii., p. 497.
[277] Quart. Journ. Geol. Soc., vol. xxvi., p. 90.
[278] My colleague, Mr. R. L. Jack.
[279] The greater portion of this chapter is from the Trans. of Geol. Soc. of Edinburgh, for 1869.
[280] [Chapter XV.], p. 253.
[281] Trans. of the Geol. Soc. of Glasgow, vol. iii., part i., page 133.
[282] Mr. Milne Home has advanced, in his “Estuary of the Firth of Forth,” p. 91, the theory that this trough had been scooped out during the glacial epoch by icebergs floating through the Midland valley from west to east when it was submerged. The bottom of the trough, be it observed, at the watershed at Kilsyth, is 300 feet above the level of its bottom at Grangemouth; and this Mr. Milne Home freely admits. But he has not explained how an iceberg, which could float across the shallow water at Kilsyth, say, 100 feet deep, could manage to grind the rocky bottom at Grangemouth, where it was not less than 400 feet deep. “The impetus acquired in the Kyle at Kilsyth,” says Mr. Milne Home, “would keep them moving on, and the prevailing westerly winds would also aid, so that when grating on the subjacent carboniferous rocks they would not have much difficulty in scooping out a channel both wider and deeper than at Kilsyth.” But how could they “grate on the subjacent carboniferous rocks” at Grangemouth, if they managed to float at Kilsyth? Surely an iceberg that could “grate” at Grangemouth would “ground” at Kilsyth.
[283] Trans. of the Geol. Soc. of Glasgow, vol. iii., p. 141.
[284] Mr. John Young and Mr. Milne Home advanced the objection, that several trap dykes cross the valley of the Clyde near Bowling, and come to so near the present surface of the land, that the Clyde at present flows across them with a depth not exceeding 20 feet. I fear that Mr. Young and Mr. Milne Home have been misinformed in regard to the existence of these dykes. About a mile above Bowling there are one or two dykes which approach to the river-bank, and may probably cross, but these could not possibly cut off a channel entering the Clyde at Bowling. In none of the borings or excavations which have been made by the Clyde Trustees has the rock been reached from Bowling downwards. I may also state that the whole Midland valley, from the Forth of Clyde to the Firth of Forth, has been surveyed by the officers of the Geological Survey, and only a single dyke has been found to cross the buried channels, viz., one (Basalt rock) running eastward from Kilsyth to the canal bridge near Dullatur. But as this is not far from the watershed between the two channels it cannot affect the question at issue. See sheet 31 of Geological Survey Map of Scotland.
[285] Trans. Geol. Soc. Glasgow, vol. iv., p. 166.