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IV.—A Revindication of the Llanberis Unconformity

Published online by Cambridge University Press:  01 May 2009

J. F. Blake
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Extract

In a paper published in the Quarterly Journal of the Geological Society for 1893, I gave an account of the evidence that led me to conclude that certain conglomerates and associated rocks occurring for some distance north-east and south-west of Llanberis, which had hitherto been considered to lie below the workable Cambrian Slates of that area, were in reality unconiormable deposits of a later date than those slates. in the year 1894 Professor T. G. Bonney and Miss 0. Raisin published in the same Journal a controversial paper criticizing my statements and conclusions.

Type
Original Articles
Information
Geological Magazine , Volume 5 , Issue 4 , April 1898 , pp. 169 - 178
Copyright
Copyright © Cambridge University Press 1898

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References

page 169 note 2 Vol xlix, pp. 441–446.

page 169 note 3 Vol. L, pp. 578–602.

page 170 note 1 Mem. Geol. Survey, vol. iii.

page 170 note 2 Q.J.G.S., vol. xxxiv, pp. 147–152.Google Scholar

page 170 note 3 Q.J.G.S., vol. xxxv, pp. 309–320.Google Scholar

page 171 note 1 All these reasons seem to me to have now disappeared. We have learned that flow-structure may he found also in an intrusive rock (see Sir A. Geikieinpostea, G, p. 93), the “slate” is a greenstone dyke, and the agglomerate may be a fault breccia. Even the proof of the felsite being of earlier age than the conglomerate would not now, if that conglomerate is post-Llanberis, prove it to be non-intrusive, and there remains only the fact that it is always followed, in regular succession, by its own debris, or what is considered to be such, and this seems sufficient.Google Scholar

page 171 note 2 Op. cit., p. 315.

page 171 note 3 Q.J.G.S., vol. xli, pp. 74–79.Google Scholar

page 172 note 1 Q.J.G.S., vol. xliv, pp. 271–290.Google Scholar

page 172 note 2 In this same paper I endeavoured to support the Cambrian age of the felsite by finding its base. Therein I mistook a squeezed relic of a dyke for slate, with the result that the section, which I thought proved my point, proved nothing, either for or against it. in a later paper (F) Miss Raisin did me the service ot pointing out this mistake, as I have much pleasure in acknowledging.

page 172 note 3 Q.J.G.S., vol. xlvii, pp. 329–342.Google Scholar

page 172 note 4 Ibid., Proc.

page 173 note 1 Q.J.G.S., vol. xlviii, pp. 243–262.Google Scholar

page 173 note 2 Q.J.G.S., vol. xlix, pp. 441–466.Google Scholar

page 173 note 3 Q.J.G.S., vol. L, pp. 578–602.Google Scholar

page 177 note 1 I might add that this is not quite like the summit conglomerate, but such arguments are of little value.