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IV.—The age of Floating Ice in North Wales1

Published online by Cambridge University Press:  01 May 2009

D. Mackintosh
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Extract

Without occupying valuable space with introductory remarks, I would begin with a description and attempted explanation of the drifts along the coast of Rhos Bay, or what is now generally called Colwyn Bay. Well-sinkings, clay and gravel pits, and coast sections, very clearly reveal a quadripartite arrangement of drifts similar to what may be seen in Cumberland. A recent well-boring at Old Colwyn went through loose gravel 9 feet; brown clay, 33 feet; and was stopped in blue clay. In Mr. Pender's brickfield, west of the Station, the pit-section and a well-boring have revealed red brick clay nearly 20 feet; sand and a little fine gravel, 16 feet; boring drill stuck fast under 60 feet of blue clay. In the ballast-pit close to the Railway Station, 30 or 40 feet of sand and gravel lie under a thin covering of red clay, the former (according to Mr. Darbishire, though this I overlooked) being underlaid by brown clay; and the sand rises up from beneath the red clay at a spot south of the road between New Colwyn and Mr. Pender's brickfield.

Type
Original Articles
Information
Geological Magazine , Volume 9 , Issue 91 , January 1872 , pp. 15 - 23
Copyright
Copyright © Cambridge University Press 1872

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Footnotes

1

Mr. De Rance must have read my articles on the North of England drifts very carelessly, or partly forgotten what he read, when he replied to me in his last article (Geol. Mag. Sept. 1871), for the reader will easily perceive that I have not said, or intended to be understood, what Mr. De Rance there attributes to me concerning the depth of water in which the blue clay of W. Yorkshire was principally accumulated—the per-centage of the larger boulders in Peel Park, Salford–the conditions existing during the Glacial period, etc. He has strangely, though I believe unintentionally, misstated what I said on the latter subject in the Geol. Mag. for July, 1871. References to some of Mr. De Rance's arguments will he found incorporated with the present article.

References

page 15 note 2 The sand or middle drift everywhere, but especially in the neighbourhood of hills, shows a tendency to raise its head suddenly above the Upper Boulder-clay, so as to appear on the same or even on a newer horizon.

page 16 note 1 They seldom exhibit marks of much flattening through grinding, though some of those which consist of limestone are so irregularly scratched all round, that a gentleman from Chester, who disbelieved in a Glacial period, contended that a party of boys had been disfiguring the boulders in play.

page 17 note 1 I fear that Miss Eyton, who has made some important contributions to Posttertiary geology, has been misinformed about the existence of blue clay around Crewe. I could see or hear nothing of it, though I found that some persons gave the name blue clay to the upper red brick clay with greyish-tinged fractures, which there overlies the middle sand and gravel.

page 17 note 2 It is not, however, the only shell-bearing clay, for shells have been found in the lower brown clay at Llandudno by Mr. Darbishire, and by others in the same clay in Lancashire and Cheshire.

page 18 note 1 A great part of the Anglesey side of the Menai Strait is covered with stratified sand and gravel. A fine section may be seen in a large pit about half way between Menai Bridge and the Monument.

page 18 note 2 I have seen no granite on the northern slopes of the Snowdonian hills, or in the Vale of Conway about Trefriw and Llanrwst, but further eastwards it would appear to have been floated some distance into the interior of the country. I have a bit of Eskdale granite which Dr. Williams, of Wrexham, found in a heap of mixed bone and stone débris which had been dug out of Cefn Cave, near St. Asaph.

page 19 note 1 Not the stupendous break-neck wedge of felstone, called Y Tryfan, at the head of Nant Francon, from going to which, in search of sea-shells, I lately prevented an eminent savant.

page 20 note 1 The Shapfell and Dalbeattie Company are quarrying granite near Dalbeattie of a somewhat different kind with a tendency to run into groups of oblong crystals of felspar of a more or less brownish hue.

page 20 note 2 Mr. Trimmer, in his Geology (1841), mentions the existence of granitic detritus at eight points between the Menai Strait and Snowdon, but he only specifies Moel-y-Tryfan, and says nothing, so far as I can remember, about the character of the granite.

page 21 note 1 According to Professor Ramsay, the shell-bearing sand and gravel of North Wales was arranged while emerging, or during terrestrial oscillations of level (Old Glaciers of North Wales, p. 95).

page 22 note 1 Professor Ramsay believes that this and a number of other lake-basins in North Wales were formed by glaciers which terminated in the sea as the land was rising, that they kept the marine drift out of the basins until they rose above the sea-level, and that the glaciers finally melting the basins were occupied by fresh water. But it may be asked, Did the cwms at the bottoms of which the lake-basins were excavated contain glaciers before the sea (through the movement of the land) had risen up to their levels? or were they only occupied by glaciers after the sea had retreated down to their levels?