374 MISS G. L. ELLES ON THE WENLOCK [May I9OO, 



Detailed Description of the Beds. 

 (i) The Llandovery Beds. 



Between the Llandeilos and the Wenlock Shales in the northern 

 part of the Builth district runs an almost continuous hand of 

 Llandovery Grit, which demands brief notice. It is easily recog- 

 nizable, and has yielded Pentamerus oblongus, Sow., P. undatus, Sow., 

 a,n& Stricklandinia lens, Sow. It seems, therefore, to represent the 

 upper part of the Llandovery Series, and rests unconformably upon 

 the Llandeilo rocks. It is well exposed at Trecoed, and in the quarry 

 at the end of Pencerrig Lake ; south-west of Pencerrig it is over- 

 lapped by the Wenlock Shales, except where it crops out on the 

 banks of the Wye. 



In every case this Pentamerus- grit is succeeded by a narrow baud 

 of soft, black, thinly-bedded shales, which differ in these characters 

 from the succeeding Wenlock Shales. Unfortunately these black 

 beds seem to be unfossiliferous, but I would suggest that they 

 possibly represent the Tarannon Shales, although in the absence of 

 entirely satisfactory evidence nothing more definite can be said. 



The grits aud shales dip beneath the Wenlock Group at an angle 

 of 25° at Trecoed, but the angle is as much as 40° in the bed of the 

 Wye. 



(ii) The Wenlock Shales. 



(a) Section north-west of Builth. 



With regard to the area which lies north and north-west of Builth, 

 it seems best to consider all the sections together; for, though 

 exposures are fairly common, there are so few continuous sections 

 that, unless the area is considered as a whole, no connected idea of 

 the sequence can be obtained. 



(1) Zone of Cyrtograptus Murchisoni, Carr. — Beds cha- 

 racterized by the predominance of G. Murchisoni form the lowest 

 part of the Wenlock Shale Series in the district. Unfortunately 

 the lowest beds of this zone are but rarely seen, since they 

 are overlapped by the higher, which in places also conceal even the 

 Llandovery Grit, and rest with <a still greater unconformity upon the 

 Llandeilo rocks. They are exposed, however, at the bottom of the 

 gully occupied by the stream which flows out of Pencerrig Lake, 

 and are seen to consist of soft, pale, calcareous shales alternating 

 with harder beds of calcareous flags. The higher beds consist almost 

 exclusively of these hard flagstones. 



The beds dip N. 30° W., at 30°. They are very fossiliferous ; 

 slabs completely covered with G. Murchisoni are common, and 

 other forms also are abundant. A list of the graptolites found 

 at this locality is given in Table I, col. A (p. 378). 



In addition to the graptolites Addas-pis Prevosti, Barr. = (Hughesi, 

 Salt.?), Orthoceras subundulatum, Portl., 0. primcevum, Eorbes, 



