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III.—On the Probable Pelean Origin of the Felsitic Slates of Snowdon, and their Metamorphism

Published online by Cambridge University Press:  01 May 2009

J. R. Dakyns ,
Edward Greenly  and
J. R. Dakyns
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Extract

There are several kinds of acid volcanic rocks in Wales. In the X neighbourhood of Snowdon there are at least five kinds, as follows:

1. There are undoubted lavas, showing lines of viscous flow and sometimes vesicular, and weathering into cubical blocks. Such may be seen on Crib Goch and on Crib Yddysgl, on Cerrig Cochion, and elsewhere. These rocks are rarely cleaved.

2. There are rocks like the last as to fracture and mode of weathering, but which are neither viscous nor vesicular. They are probably masses of felsitic dust or mud. Such may be seen in Cwm Llan.

3. There are also massive felstones, rudely cleaved, such as form Moel Meirch. and Clogwyn Llwyd.

4. There are the so-called ashes of various kinds, usually wellbedded and often highly cleaved.

5. Lastly, there are highly cleaved felsitic rocks, which show no lines of viscous flow, are generally unbedded, and which are in many places fragmentary.

Type
Original Articles
Information
Geological Magazine , Volume 2 , Issue 12 , December 1905 , pp. 541 - 549
Copyright
Copyright © Cambridge University Press 1905

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References

page 543 note 1 All the field-work upon which this paper is founded is by Mr. Dakyns. I have only visited the ground a few times.—E. G.

page 544 note 1 “Bala Volcanic Series,” pp. 16, 17.

page 544 note 2 Harker, “Bala Volcanic Series,” p. 13.

page 544 note 3 The average of eight analyses of ancient and modern rhyolites given in Geikie's, Sir A. “Text Book of Geology,” 4th ed., 1903, p. 212, is 698.Google Scholar

page 546 note 1 Greenly, Trans. Edinburgh Geol. Soc., Vol vii (1897), p. 254.

page 548 note 1 Phil. Trans. R.S., 1903: Report on the Eruptions of the Soufriere, etc., pp. 448, 470.

page 549 note 1 Mr. Harker's estimate is much greater.

page 549 note 2 “Bala Volcanic Series,” p. 121, quoting Scrope and others.

page 549 note 3 The mass ejected from the Soufriere was much greater.

A correction has been issued for this article:

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