398 MISS G. L. ELLES ON THE WEDLOCK [May 19OO, 



The basal Wenlock rocks at this locality contain the fauna 

 enumerated in Table VII, col. A (p. 399), an assemblage which 

 indicates the zone of Cyrtograptus Murchisoni. The greater part 

 of this road-section is occupied by the C '.-Murchisoni zone, except 

 where the Tarannons cross the road. Near the summit of the hill, 

 however, the M -rice art onensis zone seems to begin, though only a 

 small portion of it is exposed. 



(6) Caer Drewyn. 



The relation of the basal Wenlocks to the Tarannon Shales is also 

 well seen on the western slopes of Caer Drewyn, north of Corwen, 

 and in the small brook which runs a little east of Tomen-y-Meirw. 



On Caer Drewyn the base of the hill appears to be occupied by 

 light Tarannon Shales. Slightly higher up these pale slates are 

 seen to alternate with dark blue shaly bands, which become 

 gradually more abundant, and finally attain a considerable thickness, 

 containing the characteristic fossils of the C- Murchisoni zone. 

 These shales are well exposed in an old trial-working on the hill- 

 side ; they have yielded C. Murchisoni, Monograplus priodon, and 

 M. vomerinus. (See also Table VII, col. B, p. 399.) 



Farther north another trial-working has been made in beds of a 

 still higher horizon than that of the M .-riccartcnensis zone ; the 

 beds contain, besides M. riecartonensis, M. priodon and M. vomeri- 

 nus. The Pen-y-glog Grit succeeds the higher of these zones and 

 occupies the whole of the hilltop. 



(c) Stream East of Tomen-y-Meirw. 



In the stream east of Tomen-y-Meirw the basal Wenlock Shales are 

 also well exposed, showing alternations with pale slate-bands near 

 the junction with the Tarannons. They are not, however, very 

 fossiliferous here, and are soon faulted out against the Moel Ferna 

 Slates, which belong to the upper part of the series. 



(d) Penarth Quarry. 



Nowhere, in any single locality known to me, is the relation of 

 the Cyrtograptus-Murchisoni and Monograptus-riccartonensis zones 

 better seen than in the big quarry at Penarth (Pen-y-glog), where 

 the upper zone has been extensively quarried for slate. 



The beds in the quarry dip north-eastward, and at the south- 

 western extremity the lower beds of bluish-grey calcareous slate 

 are well seen, swarming with fairly preserved specimens of C. 

 Murchisoni and other forms characteristic of this horizon, such as 

 M. priodon, M. vomerinus var. a, and Retiolites Geinitzianus, 

 Parr. (See also Table VII, col. C\ p. 399.) 



The base of this zone is not seen'; but, as the Tarannon Shales come 

 on a little farther westward, the beds cannot be very high up in the 

 series. 



