Page:Quarterly Journal of the Geological Society of London, vol. 26.djvu/913

 probably swept away by after-denudation. Neither does any representative of the " Shirdley-Hill sand " occur in the Ribble estuary or valley, possibly because the latter was not so deep or fully formed during that period as now. But much further north, on the north shore of Morecambe Bay, at the top of a low cliff of Upper Boulder- clay, at Rampside near Barrow, is a well-known postglacial deposit, containing species of marine shells, which have been enumerated by Miss Hodgson, of Ulverstone. This deposit appeared to me in some measure to resemble a raised beach, or rather sea-bed, occurring on the southern shore of the bay, west of Pilling, between Fleetwood and Lancaster, which I found to underlie the main or thick peat of that area, and to abut against a high cliff of Upper Boulder-clay on the top of which the village of Preesall is built. The sand and shingle contain Cardium edule, Natica, and other marine shells, and fragments of haemititic iron-ore from the Furness district. The deposit is but rarely seen ; but there can be little doubt that the whole of the immense peat-moss plain forming the country on the southern side of Morecambe Bay, between the sea and the glacial-drift covered Fylde, was once the postglacial sea-bottom, and that Morecambe Bay was shaved across by the sea at the same period as the plains between the Dee and Mersey and the Alt and Douglas — the only difference being that, with the exception of the peat-moss plain between Pilling and Fleetwood, the whole of the Morecambe plain is again beneath the waves, while all the skill of the engineer has to be exerted to prevent the Alt and Douglas portion sinking below them.

When the bottom of the bay is examined, it is found to consist of red-sandstone rock, covered with a thin bed of red Boulder- clay ; this, again, is covered with a freshwater blue clay, on which grew a forest, which is covered with peat. It is clear, then, that after the postglacial sea had formed a plain in the glacial deposits, leaving cliffs all round of Boulder-clay, the whole bay became land, drainage was obstructed, and freshwater-beds were thrown down. These after- wards became terrestrial surfaces, supporting a forest, afterwards destroyed by the growth of peat, — a result exactly similar to that obtained from an examination of the estuary of the Mersey, mentioned above.

The light- coloured blue clay, occurring under the main thick peat, I have called the " Lower Cyclas-clay," as, in the neighbourhood of Southport and Formby, where it is well developed, being about 20 feet thick, it contains the shell Cyclas cornea, occasionally to the almost total exclusion of any other form. The clay does not extend eastwards under the whole of the moss, but gradually thins out along a line nearly parallel with the coast, at a distance of from three to four miles from it. To the east of this line the peat is about 12 feet thick, resting on the Shirdley-Hill sand. It is drier and more friable than where resting on the " Cyclas-clay" and is made chiefly of layers of more or less decomposed heather-stems and leaves, instead of Sphagnum and other mosses, as is the case with the peat on the clay. At the base of the peat, in both instances, a submerged forest is found. Near Halsall the trees are chiefly oak, some of them of very large

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