1^2 



DE. (j. L. ELLES 0>' THE EAEA COryiET : vol. Ixxviii, 



south ; it is most conspicuously ashy in the north (Bryn-cut and 

 Grelli-grin), and becomes less so towards the south, where ashy 

 mudstones and calcareous mudstones take its place, although 

 occasional intercalations of thin ashy bands among the mudstones 

 seem to show that thev really belon 2: to the Calcareous Ash Series. 

 AYhen all the ashy material disappears, they are practically in- 

 distinguishable lithologically from the luiderlying Allt - Ddu 

 Mudstones. 



The Pont-y-Ceunant Ash at the base of this Calcareous Ash 

 Series contains no fossils ; but the remainder of the Series is richly 

 fossiliferous, yielding many brachiopods and ti'ilobites. Among 

 the bi-achiopods OrtJiis (^Ticolella) acfonice, Triplecia spiri- 

 feroides, and Flectanibonites rliombica are the most conspicuous ; 

 0. actoiiice occurs throughout, but is particularly characteristic of 

 the limestone facies, while the TrijjJecia and Flectamhonites 

 abound in the more ashy beds. Among the trilobites Tri nucleus 

 gihhif'/'ons and Calymene caractaci are common, and JBterygo- 

 metojji'.s juJtesii is apparently characteristic of this horizon. 



Fig. 2. — Section up Bryn-cut . CHorizoYLtcd scale 

 6 inclies^l mile.) 





River Himant 



l = Allt-Ddu :Mudstones. 

 2=Pont-v-Cennaiit Asli. 

 3 = Ge]li-GrixL Calcareous Ash. 



4=rCTelli-C-;-riiL Limestone. 

 5 = Eiiiwla5 Miidstone. 



The limestone facies of this Ashy Series usually comprises one 

 or more bands of massive or concretionary, dark grey-blue lime- 

 stone, which is highly crystalline. It seems to be very pure, and 

 has invariably been worked for lime in the past, kilns being 

 associated with practically every outcrop. It sometimes contains 

 small black phosphate-nodules, and at Y Garnedd is somewhat 

 oolitic in character. It is usually a conspicuous feature in the 

 landscape Avherever it has been worked, since it shows up as a 

 rock- wall in which the purer beds have a roughened outer surface: 

 but the more thinly bedded portions show a definite honeycombed 

 appearance on their Aveathered faces : this honeycomb weathering 

 is also characteristic of the more calcareous portions of the 

 Calcareous Ash itself, though there is little resemblance between 

 the two rocks when freshlv fractured. 



