﻿146 ME. W. G. FEARNSIDES ON THE [May IQIO, 



the various papers on Cambrian rocks in general, there is little 

 evidence of actual progress of field-work within its boundaries. 

 Very important in their general bearing are papers by Salter and 

 by Salter & Hicks, 1 on the separation of the Menevian from the 

 base of the Lingula Flags, and especially the great classic of Belt, a 

 in which the remaining upper part of the Lingula Flag Series is 

 broken into the three groups, Maentwrog, Ffestiniog, and Dolgelly, 

 which are defined with all the exactitude of modern palaeontological 

 methods. 



Turning now to the subdivisions of the Ordovician System, we 

 are told 3 that in the very year (1843 or 1844) in which Sedgwick 

 had discovered the AsapJius and graptolites at Tremadoc, he and 

 Salter had also obtained Calymene parvifrons and Ogygia sehvynii 

 from beds which they called ' Tremadoc,' on the western flanks of 

 Arenig. These (Arenig) beds, however, were never correlated 

 with any member of Murchison's Shropshire series ; and, although 

 Salter had described the fossils iu 1847, it was not until 1853 

 that he determined them as of age intermediate between the 

 fauna of the Tremadoc Slates and the better-known fauna of the 

 Bala or Caradoc beds. 



In 1854 Salter went with Murchison to Shropshire, and on p. 52 

 of the second edition of ' Siluria,' which appeared about the end of 

 the year 1859, he figures fossils exactly similar to those that he 

 knew from Arenig, along with others from the lower lead-bearing 

 series of Shelve. The rocks containing them are spoken of in- 

 differently as Highest Lingula Flags or Lower Llandeilo. 



Throughout his later work in Wales, 4 and especially in his 

 Presidential Address of 1863, 5 Ramsay always insisted upon the 

 importance of the break and unconformity at the top of the Tremadoc 

 Slate of the Deudraeth, and hence must have given up any idea of 

 the synonymy between Tremadoc and Lower Llandeilo at a very 

 early date. In so doing, he must of necessity have opened the way 

 for Hicks, 6 who was working in South Wales, to supplant the 

 Murchisonian term ' Lower Llandeilo ' by the scientifically defined 

 revival of the Sedgwickian Arenig. Salter, too, in 1866, seems to 

 have been very ready for the new arrangement, and his lists of 

 Llandeilo fossils in the Geological Survey memoir (vol. iii, pp. 255-59) 

 are obviously arranged upon the Hicksian plan. The lists, however, 

 are unfortunate, in that certain beds which at Ty Obry and at 

 Tydd}^n-dicwm, within the area here described, contain Upper 

 Llandeilo (Hicks) graptolites, are identified as Lower Llandeilo, 

 and in the second edition (1881, p. 371) have their fossils included 



1 Quart. Journ. Geol. Soc. vol. xxiv (1868) p. 510. 



2 Geol. Mag. 1867, pp. 493, 536. 



3 Mem. Geol. Surv. vol. iii (1866) p. 257. 



4 Ibid. pp. 63, 71. 



5 Quart. Journ. Geol. Soc. vol. xix, p. xxxviii. 



6 Ibid. vol. xxxi (1875) p. 167. 



