Page:Quarterly Journal of the Geological Society of London, vol. 25.djvu/553

1869.] MACKINTOSH—LANCASHIRE AND CUMBERLAND DRIFTS. 429 a new village has lately sprung up) I noticed a considerable spread of decided Upper Boulder-clay. At the top of the eminence, in a quarry, a deposit of stratified sand and gravel rests immediately on the smoothly shaved-off edges of inclined beds or laminae of slate.

7. Direction and Derivation of the Flow of Granitic Drift IN N.W. Lancashire.

A line running from about Bootle in a south-easterly direction across Morecambe Bay, and along the north-eastern side of the drift plain between Preston and Longridge, would perhaps roughly indicate the north-eastern border of the granitic drift of North-west Lancashire*. In the Furness and Whicham areas I have traced it as far N.E. as Whicham Hall (as already stated), Holborn Hill, the neighbourhood of Soutergate, and Stainton Green. The north-eastern border of the ice-laden current which carried the granite would appear to have been more or less winding. The current must have set in before the close of the period of deposition of the Blackpool Lower Boulder-clay, if not earlier, and must have continued to flow till the close of the Upper Boulder-clay period. The same current may have supplied the granitic drift of the Cheshire and Shropshire plains, a great part of Staffordshire, a part of Worcestershire, &c. But if so, it seems unreasonable to look to the limited sea-coast area which Eskdale could have furnished (even admitting a series of different levels) as the sole or even the principal source of the granitic drift†. A current could not have flowed from the north over the high ground at the head of Eskdale into and along the course of the valley at the time when its granitic slopes were above water. A great current passing by the mouth of the valley, would not be likely to become loaded to a greater extent with the granite of the valley than with the rocks impinging on the previous and following parts of its course. If so, it appears difficult to explain the great preponderance of granitic boulders in many parts of the extensive drift-area just mentioned by appealing solely or even principally to Eskdale in Cumberland; and such being the case, where are we to look for the other source or sources of the granitic drift so widely distributed over the west of England? To the south of Scotland, or to some part of Ireland? Without wishing to support the theory of the Irish derivation of any part of the granite, I may state:—that the Rev. Maxwell H. Close is of opinion that chalk flints found in the drift of Shropshire came from Ireland; that I have seen chalk flints in the drift of west Cheshire nearer to Ireland; and that a chalk flint has been found at an altitude of nearly 1000 feet above the sea, on Holcombe Hill, near Manchester‡. These remarks, made perhaps partly in ignorance of

the north of this line.
 * Boulders of granite from Shap Fell may possibly be found in the drift to

† I have been informed that Shap granite may be found on the west coast of Lancashire; but this would merely show that granite may have been floated from the Shap Fells into the course of the great N.W. and S.E. current.

‡ Mr. Aitken, Trans. Geol. Soc. Man. vol. vii.

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