532 MISS CROSFIELD AND MISS 8KEAT ON THE [Aug. 1 896, 



found in the Oeratopyge-Limestone, stage Sa y , and Brinnys, sp. 

 Associated with these typical Cambrian genera is the Ordovician 

 genus Ogygia, represented by a large new species, which occurs 

 sparingly in our lower beds, becomes more common as we pass 

 higher, and finally is very abundant in beds of Arenig age. 



This mixture of Cambrian and Ordovician forms indicates the 

 position of these beds in the stratigraphical succession, and enables 

 -us to correlate them in a general way with the Tremadoc Slates of 

 North Wales and with the Shineton Shales of Shropshire. 



In the attempt to fix the horizon of these beds yet more definitely 

 we have compared our fossils with those found in Stages 2 and 3 

 in Scandinavia x ; and we observe that both the subgenera Peltura 

 and Cyclognathus properly belong to Stage 2 (Olenus-Et&ge), although 

 one species of Cyclognathus (to which subgenus our form, strictly 

 speaking, belongs) is found at the very base of Stage 3 (Asaphus- 

 Etage). 



As Peltura punctata, sp. n., is by far the commonest fossil in our 

 beds, we are inclined to consider that here we have the equivalents 

 of the lower part of Stage 3 a, which Brogger 2 has correlated with 

 the Shineton Shales. On the other hand, the presence of Orthoceras 

 throughout our beds would suggest that we have the representatives 

 ■of 3 a P or 3 a y , for this genus is not recorded by Brogger as 

 occurring below the upper part of 3 a P. Our species of Parabo- 

 linella closely resembles P. rugosa, Brog., which is confined to 3a Y . 



It thus seems unwise, if not impossible, to define the position of 

 our beds more closely than by saying that they are of the age of the 

 Tremadoc Slates, and the equivalents of part or of the whole of 

 Stage 3 a ; but as the shales are very rich in fossils, we hope that 

 additional species will ere long be found to throw further light on 

 the question. 



2. Arenig Beds. 



The presence of Phyllograptus, sp., cf. angustifolius, Hall, at Glan 

 Pibwr, and of Calymene parvifrons, var. Murchisoni, Salt., in the 

 Roman Road, and Swansea Boad upper stream, both associated 

 with Ogygia marginata, sp. n., which has come up from the 

 Tremadoc Beds, indicate the Arenig age of these mudstones ; and 

 that the graptolitic shales of Hafod-wen are of the same period is 

 •shown by the presence together of such forms as Didymograptus 

 nitidus, Hall, Dictyograptus, sp., and JEglina binodosa. These beds 

 are the equivalents of the Phyllograptus-shsles of Wales and 

 Scotland, of part of the Skidd aw Slates, of the Lower Graptolite or 

 Phyllograptus-shales of Norway and Sweden, of the Point Levis 

 Beds, and of the St. Anne Zone of Canada. 



1 Brogger, ' Die silurischen Etagen 2 und 3 im Kristianiagebiete,' 1882. 

 a Ibid. 



