Frof. T. Sternj Hunt — On Cambrian and Silurian. 459 



Agnostus, TJieca and Protospongia ; 6. grey, purple, and red flaggy 

 sandstones, witk most of the above genera, 1500 feet ; 7. grey flaggy 

 beds, 150 feet, with Paradoxides ; 8. true Menevian beds, richly 

 fossiliferous, 500 feet. The latter are the probable equivalent of the 

 base of Barrande's Etage C, and at St. Davids are conformably over- 

 laid by the Lingula-flags ; beneath which we have, including the 

 Menevian, a conformable series of 3370 feet of uncrystalline 

 sediments, fossiliferous nearly to the base, and holding a well-marked 

 fauna distinct from anything hitherto known in Great Britain or 

 elsewhere. 



The Menevian beds axe connected with the underlying strata by 

 the presence of Lingulella ferruginea, Discina pileolus, and Obolella 

 sagittatis, which extend through the whole series ; and also by the 

 genus Paradoxides, four species of which occur in these lower strata ; 

 from which the genus Olenus, which characterizes the Lingula-flags, 

 seems to be absent. To a large tuberculated trilobite of a new genus 

 found in these lowest rocks the name of Plutonia Sedgimckii has been 

 given. Hicks has proposed to unite the Menevian with the Harlech 

 beds, and to make the summit of the former the dividing line between 

 the Lower and Middle Cambrian, a suggestion which has been 

 •adopted by Lyell. (Proc. Brit. Assoc, for 1868, p. 68, and Lyell, 

 Student's Manual of Geology, pp. 466-469.) 



Both Phillips and Lyell give the name of Upper Cambrian to the 

 Lingula-flags and the Tremadoc slates, which together constitute 

 the Middle Cambrian of Sedgwick, and concede the title of Lower 

 Silurian to the Bala group or Upper Cambrian of Sedgwick. The 

 same view is adopted by Linnarsson in Sweden, who places the line 

 between Cambrian and Silurian at the base of the Llandeilo or the 

 second fauna. It was by following these authorities that I, inad- 

 vertently, in my address to the American Association for the 

 Advancement of Science in August, 1871, gave this horizon as the 

 original division between Cambrian and Sihirian. The reader of the 

 first part of this paper will see with how much justice Sedgwick 

 claims for the Cambrian the whole of the fossiliferous rocks of Wales 

 beneath the base of the May Hill Sandstone, including both the first 

 and the second fauna. I cannot but agree with the late Henry 

 Darwin Sogers, who, in 1856, reserved the designation of " the true 

 European Silurian" for the rocks above this horizon. (Keith 

 Johnston's Physical Atlas, 2nd ed.) 



The Lingula-flags and Tremadoc slates have been made the subject 

 of careful stratigraphical and palfBontological studies by the Geolo- 

 gical Survey, the results of which are set forth by Eamsay and 

 Salter in the third volume of the Memoirs of the Geological Survey, 

 published in 1866, and also, more concisely, in the Anniversary 

 Address by the former to the Geological Society in 1863. (Geol. 

 Journ. vol. xix. p. xviii.) The Lingula-flags (with the underlying 

 Menevian, which resembles them lithologically) rest in apparent 

 conformity upon the purple Harlech rocks both in Pembrokeshire 

 and in Merionethshire, where the latter appear on the great Merioneth 

 anticlinal, long since pointed out by Sedgwick. The Lingula-flags, 



