14:4: PRor. o. T. JO>'ES ox [rol. Ixxvii, 



7. The Yalexttax Seeies. By Prof. Owex Thomas Joxes^ 

 M.A., D.Sc, F.a.S. (Read April 20tli, 1921.) 



Contexts. 



Page 



I. History of the Xomenclatnre of the Yalentian Series 144 



II. Classification of the Graptolitie Facies of the Yalentian 153 



in. The Girvan 3Iixed Facies 154 



lY. Comparison of the Shelly Horizons of the Girvan Succession Tvith 



the Graptolitie Scale , 155 



Y. Comparison of the Haverfordwest Succession with that of 



Girran 158 



YI. The Llandovery District 163- 



Vll. North TVales : Corwen and Glyn Ceiriog 164 



YHI, Other Areas IGft 



(1) The Pentam^nnis oblong us or Northern Sub-Facies. 



(2) The StroiDheodonta compressa or Southern Sub-Facies. 



IX. The Base of the Yalentian 172 



I. HiSTOEY OF THE XoiIE^'CLAT^EE OE THE YaLEXTIAX SeEIES. 



The term is now commonly adopted for the rocks which lie 

 between the top of the Bala and the base of the AYenlock or 

 Salopian. These rocks have a ^\ide distribution in Wales and the 



Borders, the Lake District, and the South of Scotland, as well as 

 in Ireland and on the continent of Em-ope. They exhibit great 

 diversity of lithological and faunal characters and of thickness- 

 when traced from one district to another, and on this accomit 

 their classihcation and correlation has always presented difficulty. 

 Various classifications are in current use, but their rt^lation one to 

 the other is still ambiguous. It is with the hope of clearing 

 up some of these difficulties that the following account of the 

 historical growth of the nomenclature and the correlation of the 

 rocks has been written. 



The earliest notice of these rocks in geological literature occurs 

 in two early jDapers by Sir Eoderick Murchison,^ which were read 

 to the Geological Society of London in 1833 and 1834. 



In the earher paper the rocks below the Old Eed Sandstone 

 in the western parts of Shropshire, Herefordshire, Eadnorshire, 

 Brecknockshii'e, and Carmarthenshire are arranged as follows, in 

 descending order : — 



1. Upper Ludlow Eock. 



2. Wenlock Limestone. 



3. Lower Ludlow Eock or Die Earth. 



4. Shelly Sandstones. 



5. Black Trilobitic Flagstone. 



6. Eed conglomerate, sandstone, and slaty schists. 



1 Proc. Geol. Soc. vol. i (1826-1833) p. 474 (read April 17th, 1833); 



and vol. ii (1833-1838) p. 13 (read January 22nd, 1834). 



