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V.—Sections of Bagshot Beds at Finchampstead, Berks
Published online by Cambridge University Press: 01 May 2009
Extract
Considering the interest that has been awakened of late in the Bagshot Beds of the London Basin, and the paucity of good sections open to the light of day exhibiting any considerable vertical range of those beds, it has occurred to me that a fuller description of these Finchampstead sections may be of sufficient interest to students of Tertiary geology to justify its appearance in the pages of the Geological Magazine. In the task we have before us of attempting to workout the old physical geography of the Lower Thames Basin in later Eocene times, every contribution of facts (by no means the easiest part of inductive science) must be welcome to students of the subject. The problem was sketched in its outlines and bequeathed to his successors by the versatile mind of the late Prof. John Phillips, F.R.S. “In considering these remarkable strata (he says, of the London Bagshot Beds), which were accumulated in a period so near, geologically speaking, to our own, we are presented with problems of great interest, which, if they can be solved, will have more than local application.
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References
page 408 note 1 The Editor much regrets the delay which has arisen in the publication of this paper.
page 408 note 2 “Geology of Oxford and the Valley of the Thames,” p. 450. There is a slight error on the same page: “the highest land which [the Bagshot beds] reach in this area ” is the plateau of Cæsar's Camp and Beacon Hill south of Aldershot. not Hampstead Heath. He is, I believe, also in error in ascribing the ‘ flint-pebbles ’ to river-action so far as the rounding of them is concerned.
page 409 note 1 Q.J.G.S. vol. xli. p. 504.Google Scholar Wick Hill is named on some maps ‘Upwick's Hill.’
page 409 note 2 Q.J.G.S. vol. xlii. p. 408.Google Scholar
page 409 note 3 b,c. cit. fig. 2, p. 409.
page 409 note 4 Sections P and Q of my last paper (Q.J.G.S. vol. xliv. p. 172)Google Scholar.
page 410 note 1 For fuller details see Section L of my paper on “The Stratigraphy of the Bagshot Beds of the London Basin,” Q.J.G.S. 05, 1888.Google Scholar
page 410 note 2 A similar ‘run of the hill,’ with a pseudo-dip ‘rather north of east’ on the side of Thorn Hill, Aldershot, has been wrongly noted as a dip of the Bagshot beds there (Q.J.G.S. vol. xlii. p. 410).Google Scholar Here, however, the character of the deposit is more suggestive of rearrangement in a shallow lake; possibly on the margin of the Thames-valley arm of the great extra-morainic lake of the late Prof. H. Carvill Lewis, whose loss we deplore. To add anything to the sketch of his character at the end of the article in “Nature” (August 9th, 1888) would be an attempt to ‘gild refined gold.’
page 412 note 1 Q.J.G.S. vol. xli. p. 504Google Scholar; also ibid. vol. xlii. p. 408. There is, moreover, nothing in the known structure of the Lower Bagshot Beds of the deep-well sections of this northern side of the district to warrant the assignment of those beds to that group.
page 412 note 2 I have traced and mapped for the most part their outcrop along the northern flank of the Bagshot area from Farley Hill south of Reading to Euglefield Green (see last paper, Q.J.G.S. May, 1888).Google Scholar
page 412 note 3 Recently a new road-cutting 8 to 10 feet deep, close by North Court, has given us a capital section of the Upper Bagshot Beds. The beds are of the usual character in the lower part of the section, but these pass upwards by a steady gradation into a very stiff irony ‘leathery’ loam, in which occur numerous pipes and small layers of loose sand intermingled with many black and some green grains. They are infillings in all probability of the holes and tubes left by the decay of the roots and rhizomes of plants that grew in situ, when, after the close of the Bagshot period, the ancient marine estuary became reconverted by an ordinary silting-up process into land. Emptied of the contained sand, these holes and tubes bear a striking resemblance to those often seen in Sarsen stones (cf. remarks by the author, Proc. Geol. Assoc. vol. viii. p. 155).Google Scholar
page 413 note 1 Section O (Q.J.G.S. vol. xliv. p. 171)Google Scholar.