1843. J 261 



[The Llaasaintfraid series, including the slates and two bands of limestone, 

 lies above the poqjhyries of the Teinr river, and, consequently, far above the 

 fossiliferous beds of Pont Meibion. It is distinct from any other part of the 

 series, vrith the exception, perhaps, of the beds on the western bank of the 

 Fyrnwy river, above ZVleifod. (Fide Section VI.) It is loaded with shells of 

 the Wenlock limestone ; among which are Orthig gintuita and O. infUxta ; 

 Spirifer crispus, Teref/ratula crispata, AlryjM uffinis, and Evxnnphalus funatvs. 

 It also contains nine or ten Wenlock corals, such as Caterdpiora, &c. Among 

 the Orthides Is a new species, which is found also at Conlston. .Several of 

 the corals belong to new species. Besides the above, are several well-known 

 Caradoc sandstone species of shells. 



In addition to the above positive characters, the group is distinguished by the 

 following negative one — that it contains apparently none of the species which 

 are characteristic of the lower parts of the Protozoic series, such as Agaphtis 

 Buchii, Agnostus pigiformig, Elanus Bovrmanni, SpArifer crudalu, See 



This group, then, seems to form a kind of passage between the lower and 

 upper systems. 



To judge from the fossils only, the Coniston limestone appears to be interme- 

 diate between the Llansaintfraid and the Bala limestones.] 



On the evidence of this Section and of the lists of fossils which 

 belong to it, the author concludes : — 



1. That the highest or Llansaintfraid group cannot be identified 

 Avith any of the groups in Sections I., II., and III. ; and that if it 

 ever be brought into comparison with any group in those Sections, 

 it must be with the highest group, namely, with that which is 

 found near the crest of the southern Berwyns ; and, therefore, that 

 it lies far above the Bala limestone. 



2. That the rocks from Pont Meibion southwards, and those of 

 Craig -y-Glyn, may be brought into comparison with the lower parts 

 of the Bala series, to t?ie west of the lake, and with the slates east 

 and west of Arenig, which contain Asaphus Buchii. 



The preceding conclusions the author proposes, subject to the 

 modifications wliich they must necessarily undergo, when his 

 sections and lists of fossils come to be compared with those ob- 

 tained by the gentlemen employed on the Ordnance Geological 

 Survey, from an examination of the mountains of South "Wales 

 west of the district surveyed by Mr. Murchison. * 



* The sections of Cumberland and Vv'estmoreland are not of a nature, in the 

 author's opinion, to throw light on questions having reference to minute points 

 in the classification of the different members of the Protozoic series of rock?, 

 for, in those countries, the Lower .Silurian rocks, containing fossils, are of com- 

 paratively small thickness, and have a well-defined base, which the author has 

 form prly described. See " Proceedings of the Geol. .Soc." vol. ili. p 551. They 

 exhibit no traces of the lower beds such as occur in "North Wales, ccntaining 

 Amphm Bvchii, Sec. ; and they disappear when the Porphyries begin. The 

 Coniston limestone appears to be very little lower than the limestones of the 

 Ceiriog, and is therefore probably higher in the series than the Bala limestone. 

 In North Wales, on the contrary-, the fossiliferous series has no well-defined 

 ba.se, since fossiliferous beds of vast thickness, extending far below the Bala 

 limestone, there alternate with porphyries. 



