﻿Vol. 66.] TREMADOC SLATES OF SOUTH-EAST CARNARVONSHIRE. 145 



various subdivisions of this scheme are further denned, and we are 

 again told that the Tremadoc Slates are to be recognized by their 

 peculiar mineral structure a ; but, as great stress is laid upon the 

 occurrence of mineral veins, and of beds and concretions of magnetic 

 and pisolitic iron, it would seem that the graptolitic shales of the 

 Upper Llandeilo were still included. The definition of the Lingula 

 Flags, as extending downwards from the base of the Tremadoc 

 Slates to the sea at Trenys, would seem to be entirely satisfactory. 



The paper by Ramsay on the ' Physical Structure & Succession 

 of some of the Lower Palaeozoic Rocks of North Wales, &c.', 2 which 

 followed in 1853, has only a passing reference to the Tremadoc 

 country, but bears intrinsic evidence that the term Lingula 

 Flags was then held by the Geological Survey to include Sedgwick's 

 Tremadoc Slates, although, as 'shown by Salter's paper ' On the 

 Tracks of a Crustacean in the Lingula Flags ', 3 the district had 

 been worked over in the summer of 1852. From that time until 

 the appearance of Ramsay's great memoir on the ' Geology of North 

 Wales ' in 1866, the Tremadoc area seems to have been recognized 

 as Salter's particular preserve ; and, except for the excellent col- 

 lecting work of Homfray and Ash, all the later work seems to be 

 •due to him. 4 From the Introduction to M'Coy's ' Brit. Pal. Foss.' 

 already quoted, we learn that Salter was taken over the ground 

 by Sedgwick in 1847 and 1848 ; but, according to Salter, 5 it was 

 Barrande who, in maintaining that the Lingula Flags belong to his 

 Primordial Zone (Stage C) of Bohemia, caused him to return again. 

 By Salter also we are told that already in 1853 6 he had obtained 

 palaeontological evidence of a threefold division of the Lingula Flags ; 

 and from Ramsay 7 we learn that [after 1857] Salter was able to 

 demonstrate the value of the Tremadoc Slates as a formation con- 

 taining a distinctive fauna. 



Salter claims to have followed and mapped the Tremadoc rocks 

 and the three divisions of the Lingula Flags from Portmadoc all 

 around the anticline to Criccieth in 1860 (Mem. Geol. Surv. 

 vol. iii, 1866, p. 246). After 1860 he turned his attention to the 

 subdivision of the Tremadoc Slates ; but, although the deter- 

 mination of an Upper and a Lower division and the section across the 

 Deudraeth peninsula are in the main satisfactory, his application 

 of the results to the actual Ynyscynhaiarn area is not so easy to 

 follow. 



From 1866, the date of publication of Ramsay's ' Geology of 

 North Wales,' although we find frequent mention of the district in 



1 Quart. Journ. Geol. Soc. vol. viii (1852) p. 148. 



2 Ibid. vol. ix (1853) p. 161. 



3 Ibid. vol. x (1854) p. 208, & Eep. Brit. Assoc. (Belfast) 1852, Trans, of 

 Sections, p. 58. 



4 Mem. Geol. Surv. vol. iii (1866) pp. 67 & 242. 



5 Ibid. Appendix, p. 245. 

 G Ibid. p. 246. 



7 Quart. Journ. Geol. Soc. vol. xix (1863) p. xxxviii, & Mem. Geol. Surv. 

 vol. iii (1866) p. 7. 



1.2 



