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NORTH WALES. 



201 



con (Map 78, S.E.), about 13 miles in length and 2 miles 



wide at the broadest part. 



It lies among 



the Cambrian 



grits, conglomerates, and slates, which, near the points 

 of junction, are much altered. — See section No. 4 above, 

 and specimens Nos. 185 to 192 in this case. 



125. — Hoiinblendic PORPHYRY. — Mynydd Mawr, Llyn 

 Cwellyn, Caernarvonshire. Map 75, N.E. and N.W 



Light pink felspar base, with small specks of hornblende 

 included. 



Intruded among the Lower Silurian slates, which are 

 altered by it and rendered hard and porcelanic at the junc- 

 tion. It is about 2 miles wide, of a circular shape, and 



forms the mountain of Mynydd-mawr (or the Great Moun- 

 tain). 



126. — Reddish-brown felspathic rocks, compact or 



finely granular, with transparent quartz crystals filling 

 the cracks and cavities, and dendritic infiltrations of oxide 



f 



) 



south- 



Map 



west of Clynog Fawr, Caernarvonshire. Map 75, N. W. 



From a high cliff which rises from the sea, and forms 

 part of the intrusive masses of the Rivals, or Yr Eifl. 



127. — Felspathic porphyry. — Mynydd-tir-y-cwmmwd, 

 4 miles south- west of Pwllheli, Caernarvonshire. 

 75, S.W. Light yellowish-brown felspathic base, with a 

 few hornblende particles much decomposed, and large white 

 felspar crystals. 



Part of a mass- 5 miles in length, intruded among the 

 Bala beds. 



128.— Syenite. — Cefn Amwlch, 8 miles west of Pwll- 

 heli, Caernarvonshire. 



Map 76, S. Felspar base, with 

 white quartz crystals included, and a few specks of horn- 

 blende. 



Part of a boss of syenite, piercing Lower Silurian slates, 

 about three-quarters of a mile wide. 



129 — Syenite — Gym Goch, 11 mile south of Clynog 

 Fawr, Caernarvonshire. Map 75, N.W. Reddish-brown 



Upper 

 Gallery. 



Wall-case 4. 



