LOWER PALEOZOIC ROCKS OP HAVERFORDWEST. 487 



from the limestone of this region, it does occur in the graptolite- 

 shales of the succeeding group. 



iv. Dicranograptus-Sliales. — It has already been stated that 

 several zones must be represented among these beds, and that we 

 have been unable to work these out in the held, owing to the 

 absence of exposures continuous throughout the series. That the 

 beds do represent generall}^ the Glenkiln and lower portions of the 

 Hartfell groups of Scotland appears probable : but as we have sub- 

 mitted a large collection of specimens from this horizon to Professor 

 Lapworth, we leave the fuller determination of the age of the group 

 to him. 



The uppermost bands, which are crowded with Orthis argentea^ 

 may be compared with the Ortliis-argentea zone of Dr. Linnarsson in 

 Sweden (cf. Lapworth, Geol. Mag. dec. ii. vol. vii. p. 43). 



V. Roheston- Wathen Limestone. — The fossils of this limestone are 

 certainly of Middle Bala facies ; but trilobites are rare, and the 

 organisms are chiefly corals. The identification of this bed with 

 parts, at any rate, of the Bala and Coniston limestones receives strong 

 support from the evidence furnished by the succeeding deposits. 



vi. Trinudeus-seticornis Beds. 



(a) ShoIeshooJc Limestone Stage. — This is comparable both litho- 

 logically and palseontologically with the Ehiwlas limestone of Bala, 

 which must certainly be of different age from the true Bala limestone. 

 The bed is so peculiar in character, and maintains its appearance 

 and palseontological characters so uniformly over a wide area, that 

 it is very easy to identify, and forms therefore a very important 

 horizon for purposes of comparison. The Ehiwlas cystideans are 

 similar to those of Sholeshook, and the trilobites are mostly of the 

 same species. Stauroceplialus is present at Ehiwlas as in Pembroke- 

 sbire, and associated with it are the following fossils of the Sholes- 

 hook stage : — 



Ampyx tumidus, Forbes. 

 Cheiriirus juyenis, Salt. 

 bimucronatus, Murch. 



Triaucleus seticornis, His. 

 Leptasna tenuicincta, M'Coy. 

 Cyrtoceras sonax, Salt. 



It may be observed that, as Professor Sedgwick made his Upper 

 Bala series to include the beds above the Bala limestone, this stage 

 must be taken as the base of that series, and it forms, as observed, 

 a readily recognized base. 



In the Lake-district a bed of quite similar lithological cha- 

 racter occurs immediately above the Coniston Limestone. Its fauna 

 has not yet been fully described, but one of us has elsewhere 

 noticed it (' Sedgwick Essay,' 1882, p. 58). StaurocepJicdus is there 

 associated with the same cystideans as at Sholeshook, and a large 

 number of trilobites are common to the two deposits, and do not 

 occur in the underlying Coniston limestone. 



The starfish-bed of Prof. Lapworth (Q. J. G. S. vol. xxxviii. 

 p. 619) may possibly be the representative of this in the Girvan 

 area ; it also contains Staurocephalus glohiceps. 



In Ireland the same group of fossils appears to occur at Desert- 



2l2 



