part 2] ITS STErCTIJEE and EOCK-SrCCESSION. 167 



off : so, perhaps, if the beds were completely seen, the difference 

 might disappear. This seems all the more likely when the fauna 

 of the Dolhir Beds is studied, because it is here obvious that we 

 are dealing with a mixed fauna which naturally groups itself into 

 two, that characteristic of the Upper Caradocian containing both 

 species of ChasmopSy Calymene caractaci, and abundant Ortliis 

 {Nicolella) actonicd with two large brachiopods ; and that gene- 

 rally regarded as belonging to the Ashgillian, which contains 

 Acidaspis, species of Cheirurus and Ilemo])leurides, and small 

 brachiopods. Therefore, the large brachiopods which so frequently 

 disappear concurrently with the appearance of the Ashgillian fauna 

 do not do so in this Grlyn-Ceiriog area, remaining and occurring 

 side by side with the smaller characteristic Ashgillian tj^pes — 

 Ortliis crispa, Stropliomena corrugatella, and Bilohites hiloba. 



Nevertheless, the incoming of new types in abundance, despite 

 the absence of Phillipsinella parabola^ justifies Groom & Lake 

 in their contention that the beds are of Ashgillian age. The 

 Caradocian beds of Bala perhaps find their nearest analogues in the 

 Shropshire deposits of that age ; as the lists given on p. 171 indi- 

 cate, the fauna of the Soudley Sandstones and lower part of the 

 Cheney-Longville Flags clearl}^ belongs to the Asaphus-poioisi 

 and Ortliis {Seterorthis^-alternata fauna, and unquestionably is 

 closely related to that of the AUt-Ddu Mudstones. Moreover, the 

 Hai-nage Shales which occur below the Soudley Sandstones contain 

 Ortliograptus truncaiiis Lapworth, so that they too afford confir- 

 matory evidence of age as being referable also to the horizon of 

 the zone of Dicranograptus clingani. Whether the still lower 

 Hoar-Edge Beds should be paralleled with the Glyn-Gower Beds, 

 or whether these last should be grouped with the Allt-Ddu Mud- 

 stones and correlated with the higher beds, there is not sufficient 

 evidence to show. 



The upper part of the Cheney-Longville Beds and Acton-Scott 

 Beds, on the other hand, with their abundant Cliasmops and Orthis 

 (^Nicolella) actonicd, may readil}'- be correlated with the Grelli-grin 

 Calcareous Ash (see list, p. 170). 



Turning to the Lake District, I think it is clear that a certain 

 amount of parallelism exists between the beds of certain areas and 

 those of Bala, although the parallelism must not be pressed too 

 closely. The beds that Prof. Marr has described ^ as the Calymene- 

 Beds beneath the Ashgillian Series, in the area west of Coniston 

 Lake, are doubtless the faunal equivalents of the Gelli-grin Cal- 

 careous Ash, and the occasional specimens of the higher fauna may 

 be noted as parallel with similar occurrences in Wales. 



The Ashgillian rocks of the area are also comparable on palseon- 

 tological grounds with those at Bala ; thus the Phillip sin ella- 

 Beds of Marr contain a fauna which bears a striking general resem- 

 blance to that of the Rhiwlas Limestone and Mudstones (see list, 



^ Q. J. G. S. vol. Ixxi (1915-16) p. 191. 



