File:The Quarterly journal of the Geological Society of London (1891) (14779248334).jpg

Identifier: quarterlyjournal47189geol (find matches)
Title: The Quarterly journal of the Geological Society of London
Year: 1845 (1840s)
Authors: Geological Society of London
Subjects: Geology
Publisher: London (etc.)
Contributing Library: Smithsonian Libraries
Digitizing Sponsor: Biodiversity Heritage Library

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ches of darker rock caught up in the mass of the granite, theyappear to throw light upon the origin of several of the dykes whichpenetrate the Lower-Palseozoic rocks of the district, and which arethickly clustered in some areas, whilst they are much rarer in others.They abound within a radius of fifteen miles of the Shap granite(see Map, fig. 4, p. 290), whilst others are found in great numbersaround the other granite areas. These latter are usually felsitic,whilst those more immediately in the neighbourhood of the Shapgranite are both felsites and mica-traps, and, so far as we are aware,the latter are chiefly confined to the east end of the Lake District, * (Since this paper was read we have, by kind permission of the Director-General, compared our map with the six-inch MS. map in the Survey Office,and inserted several additional dykes in the country north ot the granite.—March 11th, 1891.) Fig. 4.—SJcetch-Majp showing the Distribution of Dijhes and Sillsaround the Shajy Granite.
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THE SHAP GK\N1TE AND ASSOCIATED BOCKS. 291 and to the Cross Fell, Sedbergh, and Ligleton areas, and do notoccur around the Eskdalo granite, though the minette of Bale Fell andthe mica-traps of Dodd are near the granite of Skiddaw. Both thefelsitic and micaceous rocks have abundant porphyritic felspars inthe neighbourhood of the Shap granite, as we have shown in ourdescription of the rocks from Stakeley Folds and elsewhere, andthese fcls23ar8 are in every respect so similar to those of the graniteitself that it seems impossible to disconnect them from that mass,especially as we find that the felspars abound near the granitecontact, and become rarer as we recede from this, whilst at thesame time the more distant dykes show other indications of havingconsolidated at a greater distance from the then deep-seated magma,as evidenced by the occurrence of vesicles in the dyke at Castle How,near Tebay, which contains few porphyritic crystals. We havealready pointed out the resemblances between

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