﻿IxXXlV [ PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [May I9C5, 



Sedgwick's Upper Bala Beds. In these circumstances the term 

 ' Caradocian' is adopted as not likely to cause any confusion — such 

 as arises, for instance, from the use of the term ' Lower Bala,' which 

 may mean either the whole of the Llandeilo or the lower part 

 of the Caradoc Series, according to the classification followed by 

 various writers. 



The plane of demarcation between Llandeilian and Caradocian 

 strata has been clearly distinguished in various parts of Britain, in 

 beds which yield almost exclusively graptolitic faunas, and also in 

 those which furnish mixed faunas. It is found between beds of 

 the former type in the Southern Uplands of Scotland, between 

 the Glenkiln (Llandeilian) and Hartfell (Caradocian) Shales, and 

 between beds of the latter type in the typical Shropshire area. 

 Details concerning the classification of these beds in South Shrop- 

 shire, where the beds are spoken of as the ' Chirbury Series,' will be 

 found in a paper by Prof. Lapworth & Prof. Watts. 1 



In the heart of Wales the lower limit of the Caradocian has 

 not yet been definitely settled. 



In the border-region of the Lake-District Prof. Nicholson and I 

 have given reasons for believing that there are two very well- 

 marked faunas of Caradocian age, belonging to beds which I have 

 elsewhere spoken of as ' the Roman-Eell Group ' and ' the Sleddale 

 Group.' 2 The latter fauna is so clearly that of the Bala Limestone 

 and associated rocks of North Wales that there is no doubt as to 

 their general contemporaneity ; but the former is an older fauna, 

 and there is some reason to suppose that it has been detected in 

 parts of North Wales, although there it has not been definitely 

 distinguished from the fauna of the higher Caradocian rocks. 



4. The Ashgillian Series. — The line of demarcation be- 

 tween the Caradocian and the Ashgillian Series may be easily 

 drawn, owing to the marked change in the faunas. 



As before stated, these Ashgillian Beds correspond generally with 

 the series to which Sedgwick gave the name ' Upper Bala,' though 

 he never defined the exact position where the line should be 

 drawn. In the Cambridge Catalogue of Cambrian & Silurian 

 Fossils he says (p. 26) : ' " Upper Bala " comprehends the Aber 

 Hirnant Beds above the Bala Limestone, with a peculiar set of 



1 'The Geology of South Shropshire' Proe. Geol.. Assoc, vol. xiii (1894) 

 p. 297. 



2 'The Coniston-Limestone" Series' Geol. Mag. 1892, p. 97. 



