Page:Quarterly Journal of the Geological Society of London, vol. 26.djvu/894

 Lower Boulder-clay has been described by two observers as resembling the Upper Till at great elevations on the Penine Chain ; but on further examination, it may possibly be found that the clay in these instances belongs to the upper division. I myself have never found any marine Lower Boulder-clay above an elevation of one hundred and fifty feet ; and I believe that the glacial sea, in the Lancashire lowlands, had only a depth of about twenty-five fathoms at the close of the period of its deposition.

Fine sections of this Boulder-clay are exhibited in the cliffs of the Ribble, above Preston, especially at Bed Scar and Balderstone, at which latter place the section was first described* by Prof. E. Hull in 1867; and I had the pleasure of showing it to Mr. Mackintosh in the spring of last year. Middle Drift. — The sand and gravel of the Middle Drift rests upon a slightly undulating inclined plane of Lower Boulder-clay, dipping from the hills of the Penine Chain towards the valley of the Mersey at Manchester, and towards the sea in the country to the west — no doubt owing to its being a plane of deposition on a sloping sea-bottom, as suggested by Prof. Ramsay to Mr. Hull, to account for a similar phenomenon in the Manchester district† — these hills, like the mountains of the Lake-district, forming islands in the Lower Boulder-clay sea.

The Middle-drift sand is well seen in the cliff at Codling Gap, near Egremont, in Wirral, where about 70 feet of Lower Boulder- clay occurs between it and the underlying pebble-beds of the Bunter Sandstone, with about the same thickness of Upper Till above ; and at the side of it the sand is much current-bedded and is extremely fine-grained, has almost to resemble the Fox-mould of the south-west of England ; it contains a fair number of pebbles, all of which are rounded, but none scratched. These generally lie in the lines of current-bedding, as is the case with the pebbles in the Triassic Pebble-beds of the district. The sand in this section is only about 20 feet in thickness, and may almost be said to be intercalated in the Boulder-clay. The rock surface here is a little below high- water mark, extending under the drift to an early, or preglacial cliff, probably about 600 yards inland at Egremont. This approaches the river and the sea at New Brighton, and forms the existing line of sea- cliff there, culminating in the well known picturesque cliff called the " Red Noses," soon after which the rock is lost sight of under a range of sand dunes.

In the Lower Boulder-clay of Codling Gap I found a shell of Turritella communis ; and Mr. Morton records the occurrence of that shell and Mya truncata in the Lower Boulder-clay of Liverpool‡. On crossing the river Mersey from Liverpool to Seacombe, and ascending the hill upon which the village of Liscard is built, the peninsula of Wirral is seen to be divided in two by a deep narrow gorge, at the bottom of which flows Wallasey Pool. This river, now


 * Trans. Man. Lit. & Phil. Soc. vol. vi. 3rd series.

† Ibid. vol. ii, 3rd. series.

‡ Geology of Liverpool, p. 15.