534 MISS CKOSFIELD AND MISS SKEAT ON THE [Aug. 1 896,, 



and also with the slates of Angers, in both of which this fossil is* 

 found abundantly in conjunction with Placoparia. These forms 

 are characteristic of the well-known Llanvirn fauna, and fix the 

 position of the shales beyond question. 



4. Didymograptus Murchisoni-sh&les. 



These are too well known to require much notice here ; they 

 evidently correspond to Hicks's Lower Llandeilo or tipper Llanvirn- 

 beds of Abereiddy Bay, and to part of Messrs. Marr and Eoberts's 

 Didymograptus-sh&les of Haverfordwest. Very few fossils were 

 found except the characteristic Didymograptus Murchisoni, Beck,, 

 and this was abundant. These beds everywhere succeed the 

 Didymograptus bifidus-shales which constitute the true Llanvirn 

 (Lower Llanvirn of Dr. Hicks) horizon. We see the same relations • 

 of the beds in Scania. Tullberg's division E, Middle Graptolite 

 Shales, has at the base a zone 0=D. Murchisoni-zone. 



^ ' ' J with Didymograptus Murcliisoni. 



y. Corresponds to part of our Didymo- 

 graptus bifidus-zone. 



5. Dicranograptus-sh&les. 



These beds regularly succeed the Didymograptus Murchisoni- 

 shales : near the base we have a zone containing Diplograptus- 

 foliaceus, Murch., and D. dentatus, Brongn. ; in a higher band 

 Climacograptus bicomis, Hall, was found. Dicranograptus ramosus, 

 Hall, occurs alone, so that the relationships of the sub-zones to 

 one another cannot yet be made out. Orthis argentea, which is 

 characteristic of the upper bands of the Dicranograpius-sh&les at 

 Haverfordwest (Quart. Journ. Geol. Soc. vol. xli. 1885, p. 478), has 

 not been found in the Carmarthen district. We have no difficulty 

 in correlating these beds with the Glenkiln Series described by 

 Prof. Lapworth, and placed by him at the very top of the Llandeilo 

 Series. Not only are the chief fossils identical, but their distribution 

 is also strikingly similar, as is shown by the following table : — 



Glenkiln Beds. 





Dicranograptus-sRAiMS. 



Dicranograptus ramosus, Hall. 

 Climacograptus bicomis, Hall. 

 Diplograptus dentatus, Brongn. 

 „ foliaceus, Murch. 



R. 

 0. 

 R. 

 C. 



R. 

 C. 

 R. 

 C. 



The same beds occur in Abereiddy Bay, at Haverfordwest, Builth, 

 Conway, in the Lake District, in County Down, and also in Sweden. 



6. Bala Beds. 



The age of the fossiliferous part of the Mount Pleasant series is 

 determined by the presence of Lingula tenuigranulata, which is 

 found elsewhere in rocks of Bala age, and is not known to oocur on 



