﻿Vol. 6 1.] AKENIO FAWR AND MOEL LLYFNANT. 615 



Dictyonema-Bsmd as the lowest division of the Tre- 

 madoc, and would place the Niobe-Beds as the highest 

 member of the Dolgelly or Upper Lingula-Fla.gs. 

 Wherever found, Dictyonema is always enclosed in dark bluish- 

 grey shale, which on inside joints is invariably filmed over with 

 iridescent iron-oxide ; also, it is always associated with spicules of 

 some sponge like Protospongia. As above mentioned, the only 

 good exposure of the Dictyonema-Band is the Old-Road section, a 

 few yards west of ISTant-ddu ; but sponge-spicules in situ and 

 Dictyonema in a loose block have been found close to the mountain- 

 fence, about half a mile due west of the summit of Moel Llyfnant. 

 The thickness of the band is quite small, and, as at Penmorfa, 

 cannot much exceed 15 or 20 feet. 



The Nant-ddu or Bellerophon-Be&s [16 pars] . 



Above the Dictyonema-B&nd is the most monotonous and un- 

 interesting series in the district. This, in the absence of any more 

 characteristic fossil, I have termed the Better op>hon-Beds. It 

 consists of a series of hard, rather dark-grey, gritty shales, usually 

 exhibiting a certain amount of incipient needle-cleavage ; and, 

 in the upper part, where the beds become softer, it has often been 

 prospected for slates. At certain horizons the shales become quite 

 calcareous, and flattened concretions of cone-in-cone chalybite up 

 to a foot or two in diameter are almost characteristic (4638). The 

 lower part of the series has yielded no trilobites, but occasionally 

 contains a few oval Lingulce, Acrotreta, and frequent, rather dis- 

 torted, undeterminable Bellerophons. The best exposure is in 

 the banks of the stream of Nant-ddu, and the entrance-cutting to 

 the old manganese-mine which was worked in these beds there. 

 Bellerophons are most abundant in the Afon Amnodd-bwll, about 

 a quarter of a mile south of Yr Orsedd. A small trial-hole for 

 slate, opened in higher beds close under the overlying Tai-Herion 

 Flags in JNant Ehos-ddu, yields also examples of a broad form of 

 Asapliellus Homfrayi, Salt., and a few distorted specimens of Olenus 

 (Parabolinella) triarthrus, Call., and 0. (P.) Salteri, Call., which 

 suggest a correlation with the lower fossiliferous horizon of 

 Belswardine Brook, Sheinton (Shineton). 



The Tai-Herion or Asaphellus-Ylsigs [15]. 



Immediately above these fossiliferous slates come the much 

 coarser and more quartzose beds, to which I have applied the name 

 of Tai-Herion or Asaphellus-~E\!ig$. These are a well- 

 marked series of hard, blue, shaly or slaty calcareous flags, and 

 contain numerous worm-tracks and castings filled with white 

 quartz-sand (4639). Certain beds among them also show remark- 

 ably well a rather curious form of ripple-bedding. In these 

 ' ripple-bedded ' rocks, alternations of coarser and finer sediment 

 take place laterally as well as vertically ; and the rock appears 



