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Published online by Cambridge University Press: 01 May 2009
In the northern half of Anglesey occur several intrusions of dark hornblendic rocks, some specimens of which were placed by Henslow in the collection made by him for the Woodwardian Museum. These rocks present a type unusual in Britain, and show some peculiarities which are of considerable interest.
A few years ago Professor Bonney found on the south-west coast of the island some boulders of a rock which he described under the name of Hornblende-picrite. It was subsequently pointed out by Professor Hughes that the probable source of these rocks was to be found in certain intrusive masses near Llanerchymedd, and indeed such boulders are scattered about rather abundantly in that neighbourhood and to the south-west. The rock in question seems, however, to be the common type of the larger eruptive masses in the north of Anglesey, and brief notes on slides cut from selected specimens taken in place may be found not unprofitable. The rocks were noticed and megascopically described in Henslow's Memoir.
page 546 note 3 Q. J. G. S. vol. xxxvii. p. 137, 1881: vol. xxxix. p. 254, 1883: vol. xli. p. 515, 1885.Google Scholar See also Teall, , “British Petrography,” pp. 81, 82; plates iv. and vi. 1886.Google Scholar
page 547 note 1 Trans. Phil. Soc. Camb. vol. i. 1822.Google Scholar
page 547 note 2 Q. J. G. S. vol. xxxviii. p. 26, 1882.Google Scholar
page 550 note 1 Amer. Journ. Sci. 05, 1887, 3rd ser. vol. xxxiii. p. 385.Google Scholar
page 550 note 2 Tscherm. Min. II. Petr. Mitth. vol. v. part ii. 1883.Google Scholar
page 550 note 3 Q. G. G. S. vol. xli. plate xvi. fig. 2, 1885.Google Scholar
page 552 note 1 The resemblance even extends to the ‘solution-planes’ in the brown hornblende, parallel to the clinopinacoid (010). The slides from Pen-y-rhiwiau, however, contain an abundance of pale grass-green actinolite in blades and fan-shaped bundles.
