Page:Quarterly Journal of the Geological Society of London, vol. 26.djvu/893

 Glacial Deposits of Western Cheshire and Lancashire.

Lower Boulder-clay. — This bed, in North Cheshire, between Liverpool and Southport, and between that town and Preston, is a soft rather loose clay, of a reddish-brown colour, containing many erratic boulders and pebbles, nearly all of which are ice-scratched, but rounded by marine action. It occasionally contains seams of sand and beds of marl, the latter being much used for marling the moss lands near Halsall, Crosby, Formby, and Southport.

When the Lower and Upper Boulder-clays are seen in the same section in the districts mentioned above, as at Egremont, in Wirral, and near Preston, the two clays are found to be apparently identical, both as regards physical aspect and the character of the included fragments. Put in the Lower Boulder-clay of Blackpool, and to a greater extent in that of the Furness district, known as "pinel," a slight change of character takes place : the stones are more closely packed, each individual stone is scratched in every possible direction, and the percentage of granites and Lake-district Silurian erratics increases. These clays lie in boss-shaped masses beneath the Middle-drift sand and gravel, as if shot down in the water by a moving body from above ; the pebbles in the clay, though so intensely scratched, are nearly all waterworn ; and fragments of the rocks beneath the drift at Blackpool are absolutely never found. It therefore appears probable that a fringe of coast-ice skirted the foot of the Lake mountains, which, lifted daily by the tides of the glacial sea, scratched the pebbles of the beach (formed by the sea before the coast-ice came into existence), in every possible direction, and that these, when the ice was carried out into the more open sea by tidal currents, were deposited in the tumultuous heaps of packed silt which we observe in various parts of the Lancashire lowlands. I may here mention that I found shells of the species of Tellina balthica and Turritella communis in tolerably good condition in the Lower Boulder-clay of the Blackpool section.

In a railway-cutting made last year between Chorley and Blackburn, the Upper Boulder-clay and Middle Drift were seen resting on a stiff clay of a bluish-black colour, containing rather angular blocks of comparatively local origin, the clay being of such extreme hardness as to seriously affect the cost of the work, damaging the tools of the men, and withstanding the action of blasting. Since examining this section, to which I have had the pleasure of directing the attention of Mr. Eccles, F.G.S., and my colleague Mr. Tiddeman, F.G.S., I have found other examples of this peculiar type of Lower Boulder-clay ; and in some cases the ordinary marine Lower Boulder- clay is seen resting on an eroded surface of the stiff blue clay beneath, which I believe to have been formed by land-ice, probably in the form of an ice-sheet. I have never yet found in it either Lake-district erratics, granite boulders, or marine shells ; and from a careful examination of the drift-deposits of the Lake-district, I believe this " terrestrial Lower Boulder-clay " to have been formed contemporaneously with the Lower Moraine Drift of that area, and that both are in great measure older deposits than the marine Lower Boulder-clay.