458 Pro/. T. Sternj Hunt — On Cambrian and Silurian. 



for like reasons divided the Liugula-flags into a lower and an upper 

 portion. For the discussion of these distinctions the reader is re- 

 ferred to the Memoirs of the GeoL Survey (vol. iii. pp. 240-257.) 

 Subsequent researches led to the division of the original Lingula- 

 flags into three parts, an upper and a middle, to which the names of 

 Dolgelly and Maentwrog were given by Mr. Belt, and a third con- 

 sisting of the basal beds, which were separated in 1865, by Salter 

 and Hicks, with the designation of Menevian, derived from the 

 ancient Eoman name of St. Davids in Pembrokeshire. It was here 

 that, in 1862, Salter found Paradoxides with Agnostus and Lingida 

 in fine black shales at the base of the Lingula-flags, resting con- 

 formably on the green and purple grits of the Lower Cambrian or 

 Harlech beds. The locality was afterwards carefully studied by 

 Hicks, and it was soon made apparent that the genus Paradoxides, 

 both here and in North Wales, was confined to a horizon below the 

 great mass of the Lingula-flags; which, on the contrary, are charac- 

 terized by numerous species of Olenus. These lower or Menevian 

 beds are hence regarded by Salter as equivalent to the lowest portion 

 of the Etage C of Barrande. 



Beneath these Menevian beds there lies, in apparent conformity, 

 the great Lower Cambrian series, frequently called the bottom or 

 basement rocks by the Government surveyors ; represented in North 

 Wales by the Harlech grits, and in South Wales, near St. Davids, by 

 a similar series of green and purple sandstones, considered by 

 Murchison, and others, as the equivalent of the Harlech rocks. 

 They were still supposed to be unfossiliferous until in June 1867, 

 Salter and Hicks announced the discovery in the red beds of this 

 lower series, at St. Davids, of a Lingulella, very like L. ferruginea of 

 the Menevian. (Geol. Journ., vol. xxiii. p. 339 ; Siluria, 4th ed. 

 jj. 650.) This led to a farther examination of these Lower Cambrian 

 beds, which has resulted in the discovery in them of a fauna distinctly 

 primordial in type, and linked to the Menevian by the presence of 

 several identical fossils ; but in many respects distinct, and marking 

 a lower fossiliferous horizon than anything known in Bohemia or in 

 Scandinavia. 



The first announcement of these important results was made to the 

 British Association at Norwich in 1868. Further details were, how- 

 ever, laid before the Geological Society in May 1871, by Messrs. 

 Harkness and Hicks, whose paper on the Ancient Eocks of St. 

 David's Promontory appears in the Geological Journal for November, 

 1871. (vol. xxviii. p. 384.) The Cambrian sediments here rest 

 upon an older series of crystalline stratified rocks, described by the 

 Geological Surveyors as syenite and greenstone, having a north- 

 west strike. Lying unconformably upon these, and with a north-east 

 strike, we have the following series, in ascending order : 1. quartzose 

 conglomerate, 60 feet ; 2. greenish flaggy sandstones, 460 feet ; 

 3. red flags or slaty beds, 50 feet, containing Lingidella ferruginea, 

 besides a larger species, Discina, and Leperditia Camhrensis ; 4. purple 

 and greenish sandstones, 1000 feet ; 5. yellowish grey sandstones, 

 flags and shales, 150 feet, with Plutonia, Conocoryphe, Microdiscus 



