Vol. 62.] TAKABTNON SERIES OF TARAUNOJf. 695 



with the exception of JRetiolites Geinitzianus, which does not make 

 its appearance in this district until the overlying Dolgau Beds 

 are reached. The Talerddig Grits, therefore, correspond to the 

 Orieston part of the Upper Gala Beds of the South of Scotland. 



Neither can the exact position occupied by the Dolgau Beds (or 

 local * Tarannon Shales ' of the Survey) be determined by any 

 reference to published lists, since their characteristic fauna has not 

 been recognized hitherto in the South of Scotland. There is, however, 

 no room for doubt that they represent the highest part of the Tipper 

 Gala, for not only are they both overlain immediately by the zone 

 of Cyrtograptus Murchisoni (the lowest zone of the Nant-ysgollon 

 Group and Riccarton Shales), but also the fauna is in every respect 

 an intermediate one between that of the Grieston and that of the 

 Riccarton Beds. They probably represent the barren beds coming 

 l3elow the Riccarton Beds in the Hawick country. The exact 

 parallelism of the Tarannon Series of this district with the Gala 

 Beds of the South of Scotland (including the zone of Rastrites 

 maximus) is thus conclusively proved. 



It is hardly necessary to insist on the identity of the fauna of 

 the lower Nant-ysgollon Shales with that of the lowest Riccarton 

 Beds ; the presence in both of the characteristic fossil — Cyrto- 

 graptus Murchisoni — places this beyond dispute. Further work 

 will doubtless show that the upper part of the jSTant-ysgollon Shales 

 corresponds to the zone of Monograptus riccartonensis. thus com- 

 pleting the parallelism between these shales and the lower part 

 of the Riccarton Group. 



It will be unnecessary to compare in detail the three Series of 

 this district with the corresponding beds of Girvan and Bohemia : an 

 examination of the lists in Tables I & II (facing p. 692) will suffice. 

 Reference must be made, however, to the deposits described from 

 the Rhayader district and Conway in Wales, the Lake District, 

 and Scania, where the beds intervening between the Llandovery and 

 AVenlock formations have been carefully zoned. 



The district of Rhayader has been worked in greater detail and 

 more recently than any other Llandovery area in Britain : there- 

 fore, a more accurate comparison of its graptolitic zones with those 

 in the Tarannon district is rendered possible. 



The Fachdre and Dolgadfan Groups correspond to theGwastaden 

 Group of Dr. Herbert Lapworth in the Rhayader district, although 

 his lowest zones are not exposed in the Tarannon country. The local 

 zone of Dimorphograptus Swanstoni can be paralleled generally with 

 his zone of Monograptus tenuis ; while that of M. fimbriatus finds its 

 equivalent in his zone of the same name. Intervening between 

 these two zones, however, there comes in the Rhayader district the 

 zone of M. cyplius. The fauna characteristic of this fossiliferous 

 band has not been recognized in the Tarannon district, thus account- 

 ing for the abrupt change in fauna observed between the Fachdre 

 and the Dolgadfan Beds. The ' cyphus '-beds are either faulted out 

 in the Pennant area, or have hitherto escaped detection. 



Q. J. G. S. No. 248. 3 b 



