part 2] 



ITS STEUCTUEE AND EOCK-SrCCESSION. 



151 



Fig. 4. — Detail of Long Quarry - 

 face, Moelfo^yn. (Vertical 

 scale: 1 incli^=.Jf\feet.) 



.;„„,Mm^r^'^'^"!^'^ 





■P////I 



Coarse asli. 



Calcareous 



ashy 

 mudstones 

 (cleaved). 



Impure 

 limestone. 



Ashy mudstoue. 



Limestone 

 grading down 

 into calcareous 

 ashy mudstone. 



Limestone. 

 Mudstone band. 



Ashy mudstone. 



Massive 

 concretionary 

 limestone 

 (worked for 

 lime) . 



end of the exposure, are seen Ehiwlas 

 stone type, while a little farther out 



Ceunant Ash has become 

 merged in the Calcareous 

 Ash Series, which is 

 extremely fossiliferous 

 throughout. The lime- 

 stone, on the other hand, 

 is well-developed, al- 

 though it is at a dif- 

 ferent horizon from the 

 limestone of Grelli-grin, 

 being in the middle of 

 the Calcareous Ash 

 Series (fig. 6, p. 154). 

 This limestone makes a 

 definite feature as soon 

 as it crops out, and is first 

 seen just a little below 

 the moor wall ; here it 

 is much bent about, 

 striking north-east and 

 south-west, north and 

 south, and east and west 

 in rapid succession. A 

 lower feature on the hill 

 seems to mark the base 

 of the Calcareous Ash 

 Series, and the Allt- 

 Ddu Mudstones are seen 

 below, all these rocks 

 being then abruptly cut 

 off by the Moel-fryn 

 displacement which runs 

 across the whole country. 

 The face of the long 

 quarry shows an excellent 

 section (fig. 4) with the 

 massive limestones at 

 the bottom overlain by 

 cleaved ashy mudstones, 

 and at the top a distinct 

 band of coarse ash, at 

 least 1 foot thick. Above 

 this band of ash there 

 is about 20 feet of cal- 

 careous ashy mudstone, 

 and immediately above 

 this, at the southern 

 Beds of the pasty mud- 

 on the moor the higher 



