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VI.—Reply to Mr. James Geikie’s Correlation of the Scotch and English Glacial Beds

Published online by Cambridge University Press:  01 May 2009

S. V. Wood Jun
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Extract

In his fourth paper Mr. Geikie sweeps the entire Glacial series of the Eastern side of England into correlation, not only with the Scotch Till, but with the Boulder-clay, both Upper and Lower, of the North-west of England. This he does, so far as I follow him, without any other grounds than that there are beds of “gravel, sand, mud and clay” in the Scotch Till. It is impossible, within the compass of these remarks, adequately to contest Mr. Geikie's views; but if the evidence of organie remains is to be regarded as worth anything, such a correlation cannot, I contend, be maintained.

Type
Original Articles
Information
Geological Magazine , Volume 9 , Issue 94 , April 1872 , pp. 171 - 176
Copyright
Copyright © Cambridge University Press 1872

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References

page 171 note 1 Some conchologists regard this shell as identical with Nucula insignis from Japan, and some with N. Lyalli, from Vancouver; while others, my father and myself among them, regard it as different from both. Even supposing, however, that one or other of these living Nuculœ be identical with Cobboldiœ, yet, for such a test as the comparison of the fauna of the East Anglian beds with that of the Scotch, it is much the same whether we regard the shell as not known living, or as living in so remote a sea as the North Pacific.

page 17 note 2 The first four of these shells are new species, figured and described in the Supplement to the Crag Mollusca now awaiting the next issue of the Palæontographical Society. Some of these may probably turn out to be living forms, which would reduce the per-centage of extinct ones. Trophon Billockbiensis may possibly be the young of Purpura tetragona, an extinct Crag species.

page 172 note 1 The Middle Glacial fauna, however, affords indications of the incoming of this North American character in the oceurrence of Venus fluctuosa, a Bridlington and North American shell net known in the Crag.

page 172 note 2 Mr. Harmer and I examined the Scotch beds on the one side of the Highlands up to Cromarty, and on the other down to Glasgow. Of course, our examination was only a hasty and superficial one; but we could see nothing beyond the difference in the constituent material, due to the different character of the rock masses of the two areas, to separate the Boulder-clay of Cromarty from the Till of the region west of Glasgow. If I am not mistaken, the Cromarty clay is merely a continuation of the Clay of Caithness, and passes up into the Highland boulder sands about the Northern end of the Caledonian Canal, as the Till does beyond the Southern end.

page 172 note 3 A larger number than 90 have been reported from these beds; but Mr. James Smith's lists are not trustworthy. I have taken my result from the revision of Mr. Smith';s authorities, made by Mr. Crosskey, with the assistance of Mr. Jeffreys. If the other (unauthenticated) shells mentioned by Mr. Smith be added, however, the fauna would not be altered at all in character, nor the proportion of it occurring in the Crag be materially varied.

page 173 note 1 Mr. De Rance argues that the Lower Boulder-clay of Lancashire must have been deposited under a submergence of only about 100 feet beneath the present sea level, because in it are fragments which he traces from rocks to the north of it, which stand at elevations of only 300 feet. If, however, as I believe, the depression of that period, instead of being 100, was upwards of 1500 feet, the ice-sheet blocking out the sea and resting on these 300 feet elevations would convey fragments from them into the Boulder-clay then forming at the seaward edge of the ice. In a similar way, I now believe that the débris of the Chalk was carried into the great Chalky Clay when the highest elevations of the Chalk country were below the sea level, and that the second representation of my triple section, at p. 90 of the 24th Volume of the Geological Society's Journal, instead of being drawn to the 700 feet level, might, by thickening the ice-sheet, be drawn to the same 1500 feet level as the third, the resulting phenomena being due to the retreat of the ice alone without additional subsidence.

page 174 note 1 Elephas primigenius and the horse are mentioned by Prof. Phillips as having occurred in abundance in the gravel below the Hessle clay at Hessle.