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II.—The Chalk Bluffs at Trimingham

Published online by Cambridge University Press:  01 May 2009

T. G. Bonney  and
E. Hill
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Extract

The huge masses of chalk in the glacial drift on both sides of Cromer, and especially at the headland near Trimingham, have for many years attracted the attention of geologists. In this Magazine (Dec. II, Vol. VII, 1880, p. 55) and in the Survey Memoir on the Geology of the Country around Cromer, published in 1882, Mr. Clement Reid ascribes those at the latter place to the advance of an ice-sheet by which the chalk has been thrust up into a kind of fold and the flint layers have been bent, illustrating his interpretation by a diagrammatic section. We visited the Cromer cliffs for the first time in 1892, and after a careful examination of the Trimingham headland, not only felt more strongly than before certain weak points in Mr. Reid's reasoning, but also observed some facts difficult to reconcile with his conclusions. Since that date we have more than once visited these sections, and found last April that comparatively recent inroads of the sea had made great changes which had shown the relations of the chalk and glacial drift to be, in our opinion, incompatible with Mr. Reid's interpretation.

Type
Original Articles
Information
Geological Magazine , Volume 2 , Issue 9 , September 1905 , pp. 397 - 403
Copyright
Copyright © Cambridge University Press 1905

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References

page 398 note 1 We prefer this more general term to that of till, by which it has generally been designated in the Cromer sections. Though the latter is no longer used to imply an indubitable product of land ice (a very convenient distinction), some remnant of that connotation still clings to the word, and besides this we are unable to see in what important respect (except an occasional more distinct appearance of stratification) these glacial clays near Cromer differ from similar English deposits to the north, south, or west.

page 398 note 2 Meaning such as is figured in the Memoir. Throughout we paid more attention to the western bluff (hence the above use of the singular) because the bent flint layers in that made it the mainstay of the hypothesis.

page 399 note 1 One of us (T. G. B.) records in his diary that this chalk-mass seemed to be included in the boulder-clay which cropped out on the shore about four yards to the west; that it contained Belemnitella mueronata, and that the flints, though rather discontinuous, seemed to form a C-like curve (on this detail, however, we were not quite agreed). He records chalk as exposed to west and to east of the eastern mass, but whether connected with it or as separate boulders could not be determined.

page 399 note 2 Two varieties of boulder-clay occur in the Cromer district, one of a bluish-grey colour, another rather browner, more sandy, more distinctly stratified, and sometimes less pebbly. West of Cromer the latter is the commoner; east of it, on the whole, we think, the former, which is often the lower in position, but sometimes the one seems to pass into the other, or even to replace it.

page 400 note 1 See Plate XXII, a reproduction of a photograph, taken shortly after our visit by Mr. R. T. Mallet, for which and several others of great interest we are indebted to his kindness. By the aid of this our description, we trust, will be intelligible to the reader.

page 400 note 2 It was not accessible.

page 400 note 3 Wedge-like ends are not uncommon in these great chalk boulders.

page 400 note 4 In the neighbourhood of these masses, when the tide permitted (which sometimes it did not), we have seen chalk near one mass, clay near the other, but no proof that they are continuous with the chalk platform, which undoubtedly lies a very few feet below them. A memorandum sent us with the photograph by Mr. Mallet is important. “ The foreground is a large mass of blue till, on the level top of which the camera was placed. It was about a foot above the sea at 4 p.m. on May 9th.” (About an inch vertical of this foreground has not been reproduced in the Plate, for otherwise the scale must have been diminished.)

page 401 note 1 A third and smaller chalk-mass was exposed in the cliff ahout twenty yards still further east.

page 401 note 2 Quart. Journ. Geol. Soc., vol. xxxiv (1878), pp. 563–566.

page 402 note 1 Quart. Journ. Geol. Soc., vol. lv (1899), p. 305, and vol. lvii (1901), p. 1.

page 402 note 2 It takes the shape of a fairly open hook, the two arms forming rather less than a right angle; the ‘ horizontal’ part of it slopes slightly westward; a thin extension of a rather sandy houlder-clay dies out beneath it, and then the chalk probably touches (this part was masked by some talus) the Leda myalis sand.