180 



Upper 

 Galleey. 



"Wall-case 4 



8. 



IGNEOUS ROCKS, NORTH WALES. 



Compact felspatiiic ashes, talcose. 



. Mynydd 



Gader, Dolgelli, Merionethshire. Map 59, N.E. Vary. 



ing from finely granular to compact felspathic ashes. Red- 



dish or brownish-grey, weathering to a light greenish-grey. 



From the same strata as Nos. 5, 6, and 7. 



9. — Calcareous felspathic poiipiiyritic ashes, talcose. 



■Llyn Aran, Cader Idris, near Dolgelli, Merionethshire. 



Consisting principally of entire and broken 

 mr embedded in a talcose and felspathic 

 base, and including filmy layers of black slate, slightly cal- 

 careous (from infiltration ?). Weathers of a dark brown 



N.E 

 of/. 



colour : 



when newly fractured, colour dark bluish-green. 



The upper portion of the thick beds of ashes which 

 underlie the crystalline traps of Cader Idris exhibits a 

 mixture of ordinary slaty sediment with felspathic and 

 talcose. ashy material, which originally consisted of fine 

 volcanic dust and broken crystals of felspar. 



The rocks immediately north-west of the Dolgelli and 

 Bala road are repeated by a great fault at the river Wnion, 

 which is a downthrow on the north-west. See section 

 No. i above. This fault passes from the neighbourhood of 

 Dolgelli by the Bala road through Bala lake, repeating the 

 rocks of the Cader Idris 

 shown in the section. 



10. — Felspathic sandy and slaty beds, black slaty 



hands, interstratified with dark grey felspathic layers, which 

 are unequally affected by cleavage. — Moel Offrwm, near 



and Aran range in the manner 



Me 



Map 



Idri 



This and the rocks up to No. 1 3 are from the geological 

 equivalents of the lower part of the thick beds of ashes 

 which underlie the crystalline felspathic trap of Cader 



>. On Moel Offrwm the ashy beds are mixed with a 

 large quantity of ordinary slaty and sandy sediment. 



!!• — Highly indurated felspathic sandstone. — Moel 

 Offrwm, near Dolgelli, Merionethshire. Dark blackish- 

 green finely granular rock, with a flat conchoidal fracture. 

 Weathers to dark brown. 



From the same beds as No. 10. 







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