234 REPUTED GRANITE OF ANGLESEA. 



dark-green hornblende, occasionally with pyrites and epidote. Occa- 

 sionally felsite veins occur in the rock, which is divided up by three 

 or four systems of joints. Under the microscope the quartz and 

 felspar are occasionally inter-crystallised, as in the syenite. 



The felspar is chiefly orthoclase, but is mixed with oligoclase. It 

 is inferred by Professor Bonney and Mr. Hill that all these rocks of 

 Charnwood Forest were intruded at about the close of the Silurian 

 period, and are of the same age as the granites and syenites of the 

 Lake country. 



Diorite. To the north of Brazil Wood is a knoll of dark diorite 

 which consists of white plagioclase felspar and hornblende. 



Granite of Anglesea. The reputed granite of Anglesea furnishes 

 a notable instance of the way in which the nomenclature of rocks 

 sometimes changes, with a new interpretation, for most recent writers 

 deny that the island contains any granite at all. 



According to Sir Andrew Ramsay the granite runs across the 

 island in a broad irregular belt nearly 12 miles long. Its greatest 

 width is less than 3 miles. Where best developed it is composed of 

 quartz, felspar, and black and silvery mica, but it is usually coarse, 

 with the felspar not well crystallised, and the mica often absent. It 

 is regarded by Dr. Hicks as a Dimetian rock. All along the south side 

 towards Caernarvon Bay, it is bordered by a belt of hard felspatho- 

 silicious-looking rock, sometimes faintly laminated or more clearly 

 foliated. This band Dr. Hicks names Halleflinta, and identifies as 

 Pebidian. Near Bodwrog portions of foliated rocks are interlaced 

 with the granite, and further west there is a mass of altered rocks 

 entirely surrounded by granite. The foliated semi-crystalline rock 

 often almost melts into the granite. Elsewhere it passes insensibly 

 into foliated hornblendic gneiss. On the west the boundary between 

 the granite and gneiss rocks is equally obscure. In some places 

 innumerable granite veins ramify into the gneiss, and so alter it that 

 the two rocks are inseparable. Round Handrygarn much of the 

 granite is hornblendic. Professor Eamsay remarks that it was im- 

 possible not to be impressed with the idea that the granite and its 

 veins are merely the result of a more thorough metamorphism than 

 was attained in the production of the associated gneiss. And he 

 observes that the stratified rocks near to its margin dip indifferently 

 towards it and from it, as if part of the strata had been used up in 

 the making of the granite itself. In the west of the island, near 

 Llan-Trefwll, there is a small patch of granite, round which the Cam- 

 brian rocks are much altered, and several small hornblendic patches, 

 which were formerly regarded as greenstones. West of Treath Dwlas 

 a larger granitic mass stretches two miles inland. 1 



1 Ramsay, North Wales. These rocks have since been described by Dr. 

 Hicks, Quarterly Journal Geological Societ}% vol. xxxv. p. 295, as Precambrian. 

 Professor Bonney terms the rock Granitoid gneiss, and gneiss. Dr. Callaway 

 (Q. J. G. S., vol. xxxvii. p. 210) names much of the rock Granitoidite. 



