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IV.—On the Drifts of the West and South Borders of the Lake District, and on the Three Great Granitic Dispersions

Published online by Cambridge University Press:  01 May 2009

D. Mackintosh
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Extract

Boulder-scars.—From Maryport to Parkgate, the E. coast of the Irish Sea at intervals exhibits accumulations or concentrations of large boulders, which are locally called scars. They may be seen in all stages of formation, from the denudational area, where they are in course of being left by the washing away of the clayey matrix, to the depositional area, where they have become half-covered with recent sand and shingle. In many places (as between Seascale and near Silecroft) there are so many boulders within a small area as to show that a considerable thickness of the clay must have been removed. With the exception of having tumbled down as the cliffs were undermined and worn back by the sea, many of the boulders may still rest nearly in the positions they occupied in the clay, but (as is evidenced on the coast at Parkgate) others, up to a great diameter, may have been shifted horizontally. Some of the scars exist where the Boulder-clay would appear to have risen up into ridges or mounds, as no clay is now found opposite to them at the base of the sea-cliff. Others are clay and boulder plateaux, visibly connected with the cliff-line. Most of the scars, I believe, are remnants of the great Lower Brown Boulder-clay. The most conspicuous boulder in the scars S.W. of Bootle, is Eskdale-fell granite, accompanied by a little Criffell granite, and a great number of the usual felspathic erratics.

Type
Original Articles
Information
Geological Magazine , Volume 8 , Issue 85 , July 1871 , pp. 303 - 312
Copyright
Copyright © Cambridge University Press 1871

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References

page 304 note 1 The boundary in Furness, and in many places further North and South, must have teen more or less deeply submerged, and one cannot long trace drift-boundaries without having to abandon the notion that they must always have been marked by dry land, or that dry land necessarily existed where there are driftless areas.

page 307 note 1 In E. Lancashire, along the boundary of the great North-western drift, boulders have found their way into valleys lying at nearly right angles to the general course of the drift. Far up in the narrow valley called Swineshaw, near Staley Bridge, there are many stones of Eskdale granite and Wastdale granilite which reach a height of 900 feet above the sea. They are associated with stones which must have come from various points of the compass.

page 308 note 1 I may here remark, in answer to Mr. de Rance, that while in Bowness and the neighbourhood, I ascertained from various persons, who were thoroughly acquainted with all the ins and outs of the lake, that none of the detritus or sediment brought in by the Brathay river can find its way through the lake to the lower end, and thence to the sea; and one reason assigned was that the currents generated by wind, etc. (which often reach a great depth, as proved by net sinking), more frequently flow from the S. or up the lake, than from the N. Lacustrine deposits, which have all resulted from the action of fresh-water, afford the only true measure of subaërial degradation since the Glacial period.

page 308 note 2 I never saw any Shapfell granite farther S than the road between Yealand and Silverdale. Professor Phillips mentions its occurrence in a canal S. of Lancaster. Within the area of the great North-western drift, farther south, a certain kind of Dalbeattie (Criffell) granite might be easily mistaken for Shapfell.

page 310 note 1 The finest sections of sand and gravel I have yet seen are at the Carnforth Railway Station, and on the Canal side. At the latter place there is gravel above and below, and sand in the middle. At the village, a great deposit of sand contains enormous limestone boulders, one of them 9½×9½×5 feet. In addition to limestone, in the Carnforth drifts, there are Silurian grits and volcanic rocks from about N.N.E., and Carboniferous grits, etc., from the N.E.

page 310 note 2 Geol. Mag., August, October, December, 1870, and February, June, and July, 1871Google Scholar; Proceed. W. Riding Geol. Soc., 1870Google Scholar; Quart. Journ. Geol. Soc. vol. xxv.Google Scholar

page 311 note 1 According to Forbes no actual glacier is capable of smoothing or polishing boulders, though by means of a gritty base it may smooth and polish rock-surfaces.