182 



IGNEOUS ROCKS, NORTH WALES. 



gS. Which are re P laced b J ochreous matter. Weathers 

 Wail^se 4. ,rre ? ularl 7 of a %kt greenish-grey colour. Emits a 



argillaceous odour. 



These beds form the top of Arenig-fawi\ (S 



very- 



No. 9, 



) 



They are often largely and distinctly 

 bedded, but sometimes much jointed and massive, and also 

 when undecomposed, so much resemble the melted traps 

 that for short spaces they are not easily separated. Fre- 

 quently they are porphyritic, even where most distinctly 



bedded. 



) 



18. — Porphyritic felspathic ashes (decomposing).^ 

 Mynydd Nodol, five miles west-north-west of Bala, Merio- 

 nethshire. Grey felspathic rock, with white specks and 

 patches of decomposing felspar. Weathers of a light brown 

 colour. Emits a strong argillaceous odour. 



This specimen is from the same set of thick ashy beds 

 that form the Arenig, &c. See description of No. 13. 



19 - — Tltin bedded, compact, greenish-grey ashes 

 slightly porphyritic ; weathering light brown. East side of 

 Y Graig, about eight miles south-west of Bala, Merioneth- 



shire. 



fine felsp 



This and the two following specimens are from parts of 

 the highest bods of this volcanic series. 



20.— Compact felspathic ashes.— East slope of Arenig, 

 Merionethshire. Dark grey, finely laminated felspathic 

 rock. ^ Weathers of a light grey or brownish -hWlr 



This rock forms the top beds of Arenijr. 





21. — Bedded felspathic porphyry. 



Me 



fragment 



Llyn Arenig, 

 Compact, dark greenish-grey rock, with 

 •ystals of felspar and grey felspathic and 

 Weathers very unequally, the included 

 fragments projecting from the surface of the mass. 



In hand specimens, this rock might be mistaken for a 

 porphyry that had been melted. On the spot its bedded 

 character tells its true origin. 



22. 



Porphyritic ashes, calcareous 



felspathic 



West of Moel Llyfnnant, Merionethshire. Map 75 



1 



: 



ask 







lie A 

 I 



IP 



;t)l 



ri 



kl 



18 1 



II 



■ 



15, 



i 



. 



