. The Quarterly journal of the Geological Society of London. whichappears to have been opened up by blasting comparatively all appearance, this rock resembles the ordinary basic dvkes whichpenetrate the quartz-felsite in this locality, but it has evidentlvbeen much sheared. 1 T. G. Bonney & C. A. Raisin, On the Belatious of some of the OlderPragmental Rocks in North-Western Caernarvonshire Quart. Journ Geo!Soc. vol. 1 (1894) p. 578. 2 On the Cambrian & Associated Rocks in North-Western Caernarvonshire Ibid. vol. xliv (1888) pp. 283, 284. 3 On the Lower Limit of the Cambrian Series
. The Quarterly journal of the Geological Society of London. whichappears to have been opened up by blasting comparatively all appearance, this rock resembles the ordinary basic dvkes whichpenetrate the quartz-felsite in this locality, but it has evidentlvbeen much sheared. 1 T. G. Bonney & C. A. Raisin, On the Belatious of some of the OlderPragmental Rocks in North-Western Caernarvonshire Quart. Journ Geo!Soc. vol. 1 (1894) p. 578. 2 On the Cambrian & Associated Rocks in North-Western Caernarvonshire Ibid. vol. xliv (1888) pp. 283, 284. 3 On the Lower Limit of the Cambrian Series in Xorth-Western Caer-narvonshire Ibid. vol. xlvii (1891) p. 337. 376 ME. J. V. ELSDEN OX THE AGE OF [Aug. 1904, The contacts with the felsite on each side look fairly clean andregular; but, near the centre of the exposure, which is about 10 feetwide, the greenstone is penetrated by a tongue of felsite, about2 inches broad near the upper exposed part, and tapering to apoint at the lower extremity2 feet. Che length of this tongue is about ^ 1 ^^ -to. A thin slice of this rock, if examined beneath the microscope,presents the appearance of a quartz-felsite, and resembles in allessential features the descriptions given by Prof. Bonney of thefelsites of this The section shows irregular subangularblebs of quartz, giving somewhat undulose extinction, and 1 T. G-. Bonney, On the Quartz-Felsite & Associated Rocks at the Base ofthe Cambrian Series in North-Western Caernarvonshire Quart. Journ. vol. xxxv (1879; pp. 311 ct seqq. Vol. 60.] THE LLYN-PADARN DYKES. 377 enclosing portions of the cryptocrystalline groundmass. The latteris granular, and appears to consist almost entirely of quartz, andpossibly some felspar. There are also numerous laths of a greenish,strongly-pleochroic mineral, with slightly-oblique extinction, whichmay be microliths of hornblende. There is much opaque granularmatter, and some chloritic patches occur. The rock is apparentlymodified slightly by c
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Keywords: ., bookcentury1800, bookdecade1840, booksubjectgeology, bookyear1845
