520 ME. 0. T. JONES ON THE HAKTEELL-VALENTIAN [Nov. 1909, 



grove and Capel Dewi on the north side of the valley, and about 

 Capel Sion on the south side. The Lovesgrove beds dip east- 

 wards, and are underlain by dark-blue shales and mudstones, 

 which probably floor the drift-covered strike-valley followed by the 

 Cambrian Railway. Similar grits and shales appear again on the 

 hills to the west of that railway, and in them is the Cefn Hendre 

 Quarry, from which Walter Keeping recorded many graptolites. 

 This quarry was exhaustively searched on more than one occasion, 

 and a large number of specimens of Monograptus cf. exiguus was 

 obtained, associated with M. nodifer(l), a single specimen of 

 M. turricidatus, and other poorly-preserved species which I was 

 unable to identify. 



The abundance of the first-named form suggests a comparison with 

 the Myherin Mudstones, where that form commonly occurs. It was 

 not recorded by Keeping, which is rather strange, considering that 

 at present it is difficult to find any other graptolite in the quarry. 



Between Cefn Hendre and the coast the Aberystwyth Group 

 comes on, with its typical characters ; bands of dark-grey evenly- 

 bedded grit, from 6 to 12 inches thick, alternate with thin bands of 

 soft dark-blue mudstones, usually cleaved. This type undoubtedly 

 denotes a higher horizon than the Cefn Hendre Quarry. 



At the foot of the Alltwen Cliffs, west of Tanybwlch, I was so 

 fortunate as to discover several graptolites in some of the mud- 

 stones ; the commonest form was Monograptus priodon, and with 

 it were M. nudus, M. turriculatus, and M. cf. salteri. The first- 

 named can be obtained also in the large quarry near the Harbour. 

 A single specimen of Petalograptus palmeus var. tenuis was collected 

 by Mr. D. C. Evans (St. Clears), from the grit-quarries near Trinity 

 Church : and a graptolite which may be referred to Monograptus 

 nodifer was found by myself in the Cwm "Woods Quarry, north of 

 Aberystwyth. From the abundance of M. priodon in these strata, 

 and the presence of M. turricidatus, this fauna compares with that 

 of the highest Ela'en Myherin Mudstones and the Rhuddnant Group; 

 or it may perhaps denote a still higher horizon. 



The Cefn Hendre beds are lithologically very similar to the Grit 

 Group which commences at Llyn Rhuddnant ; there appears con- 

 sequently to be some discrepancy between the lithological and the 

 paliEontological evidence, suggesting that the conditions of the 

 Aberystwyth Grit Group commenced somewhat earlier on the west 

 of the anticlinorium than on the east. The Aberystwyth Grits, in 

 their typical development, are not represented on the east of the 

 anticlinorium north of the Ystwyth Valley ; but they can be matched 

 exactly far to the south of that valley, where the structure would 

 lead one to expect higher strata than those which occur on the 

 north. It is clear, however, on lithological and palseontological 

 grounds, that the Aberystwyth Grits occupy a high horizon in the 

 Ystwyth Stage, and are, in fact, the highest beds that occur in 

 the district : this involves a considerable change from the position 

 assigned to them by Keeping, who regarded them as the lowest beds, 

 far lower than the Grits of Plynlimon. 



