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III.—The Rhythmic Deposition of Flint

Published online by Cambridge University Press:  01 May 2009

Grenville A. J. Cole M.R.I.A., F.G.S.
Grenville A. J. Cole M.R.I.A., F.G.S.
Affiliation:
Royal College of Science, Dublin.
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Extract

Mr. G. W. Bulman, in an essay on “Chalk Flints and the Age of the Earth”, states that Professor Owen regarded the layers of flint in chalk as “the remains of successive crops of sponges which grew again and again according to some periodic law”. Mr. Bulman then observes that the only periods affecting rock-formation are annual, and he suggests that sponge-growth might be rapid during the summer months and that free-swimming reproductive spores might be liberated towards winter, the old sponges then dying off. This implies that the water at the depths in which the sponges lived in our Cretaceous seas was responsive to climatic change, and that the sponges were equally responsive. The suggestion breaks down, however, on another ground, when its author points out that it demands the deposition of 3 or 4 feet of chalk in a year, so that the whole of the English strata above the Albian might have accumulated in about four centuries. Mr. Bulman thereupon remains hesitant and enquiring.

Type
Original Articles
Information
Geological Magazine , Volume 4 , Issue 2 , February 1917 , pp. 64 - 68
Copyright
Copyright © Cambridge University Press 1917

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References

1 Science Progress, No. 41, p. 154, 07, 1916.Google Scholar

2 The Students& Elements of Geology, p. 265: 1871.Google Scholar

1 “A Contribution to the Physical History of the Cretaceous Flints”: Quart. Journ. Geol. Soc. London, vol. xxxvi, p. 68: 1880.Google Scholar

2 Op. cit., p. 82.

3 Op. cit., Science Progress, No. 41, p. 156Google Scholar.

1 “The Causes of Variation in the Composition of Igneous Rocks”: Natural Science, vol. iv, p. 139: 1894Google Scholar.

2 “Eozoönal Structure of the Ejected Blocks of Monte Somma,” Sci. Trans. R. Dublin Soc., vol. v, p. 264: 1894Google Scholar.

3 The concentric rings of flint in the chalk of Cromer, described by Clement Reid on p. 4 of The Geology of the Country around Cromer (Mem. Geol. Surv.: 1882), seem a case of diffusion of silica outwards from certain centres in a stratum about a foot in thickness. One of these rings has a longer diameter of 15 feet; others are perfect circles 9 feet in diameter. The two concentric circles figured in the memoir certainly suggest rhythmic deposition. It would be interesting to know what physical character of the beds above and below has prevented the rings from developing into spherical shells.