200 



INTRUSIVE IGNEOUS ROCKS. 



Upper 

 Gallery. 



Wall-case 4. 



Part of a line of greenstone intruded between beds of the 

 Lingula flags. The rocks are altered both above and below 

 the greenstone proving its intrusive character. 



119. — Greenstone. — Bwlch-y-Hendref. As above. 

 Dull greenish-black rock, obscurely laminated in structure 

 made up of acicular felspar crystals and plates of hornblende 

 in alternate layers, the former projecting on the weathered 

 surface. 



Greenstone. — Bryn Prydydd, 4 miles north 



Map 75, S.E. Greenish-grey 



120. 



Me 



rock, made of an intimate mixture of light and dark green 

 hornblende and potash felspar indistinctly crystallized, with 

 strings of felspar traversing the mass. 



From a mass of greenstone intruded among the Lingula 



flags. 



121. — Greenstone. — Bwlchau yr-Figen, 3 miles north- 



Mowdwv. Mer 



Map 



Finely granular mixture of felspar and dark coloured horn- 

 blende. 



From one of several lines of greenstone intruded into the 

 felspathic trap of the Aran range. 



122.— Calcareous greenstone. — Ffestiniog, Merioneth- 

 shire. Map 75, N.E. Intimate mixture of felspar and 

 Tery small hornblende crystals, with kernels of calc spar. 



From one of many dykes intruded into the Lingula flags. 



123. — Calcareous dyke. — Blaen y-ddol, half a mile north 

 of Ffestiniog, Merionethshire. Map 75, JS.E. Compact 

 grey felspathic rock, with slaty cleavage, somewhat cal- 



careous. 



Same as above. 

 124. — Quartz 



shire. Man 78, S 



porphyry. — Llyn Padarn, Caernarvon- 

 .E. Decomposing felspar, nearly china 



clay, full of granular quartz crystals, mostly stained brown 

 or yellow. Strings of quartz traverse the mass. It is an 

 altered condition of JS 7 o. 185. 



mass which extends from 



Part of a large intrusive 



Llanllyfhi (75, N.W.) to St. Ann's Chapel, Nant Fran- 



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