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IV.—Note on a Granite Junction in the Ross of Mull

Published online by Cambridge University Press:  01 May 2009

J. G. Goodchild
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Extract

In a review of Nicholson's “Geology of Cumberland and Westmoreland,” which appeared in the GEOLOGICAL MAGAZINE about a quarter of a century ago, the reviewer observes, in referring to some remarks upon the Shap Granite, that this and other granites have clearly taken the place of the rocks whose position they occupy, and that, in fact, intrusive rocks can be shown, in a great majority of instances, to have replaced, rather than to have displaced, the rock masses which they invade. The reviewer's identity with a wellknown Professor of Geology at one of the English Universities is sufficiently evidenced by his intimate acquaintance with the geology of British Silurian and Cambrian rocks.

Type
Original Articles
Information
Geological Magazine , Volume 9 , Issue 10 , October 1892 , pp. 447 - 463
Copyright
Copyright © Cambridge University Press 1892

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References

page 447 1 note In support of this statement, I may quote a remark made by Mr. Goodchild in a paper read before the Geologists’ Association on July 5th, 1889, in which he refers to the paper by Professor Nicholson and myself on the Stockdale Shales. “If we listen to our palæontologists we must classify the Graptolitic Mudstones with the Ordovicians; while, if we are guided by the physical evidence alone, then the Graptolitic Mudstones with their Ordoviciau fauna must go in the same group with the beds above, and be classed as Silurian.” If Mr. Goodchild had studied our paper, he would have discovered that the Graptolitic Mudstones (there called the Skelgill Beds) do not contain a single Ordovician form, with the possible exception of Climacograptus normalis. Again, in the same paper Mr. Goodchild states that during the accumulation of the Browgill Beds “deep oceanic conditions prevailed, and the old colony of graptolites either migrated still further, or else it became completely extirpated here.” A glance at our paper would have shown that two well-marked graptolitic zones occur in the Browgill Beds of the Cross Fell area, and that the graptolites of these zones are intermediate between those of the Skelgill Beds and those of the Lower Coniston Flags, which according to Mr. Goodchild “migrated from a different zoological province!” Mr. Goodchild's depressions, elevations, and migrations belong to a past generation who made much of “Colonies” and similar ingenious explanations; but it is refreshing to meet with them again, after the accurate work on Graptolites of Lapworth, Linnarsson, Tullberg, and others.

page 447 2 note A reference to the same phenomena is given in the Geological Survey Memoir on the Sedbergh District, in connection with some minette dykes there.

page 451 1 note It should be noted that as this upper part is that which is most readily denuded away during subsidence beneath the waves, true laccolites can be but rarely preserved in a fossil state.