48 CAMBRIAN. 



Wales were studied by Sedgwick during the summers of 1831 and 

 1832, and in the following year he gave the name Cambrian to the 

 great mass of the slaty rocks and limestones in North Wales, ex- 

 tending from the Menai Straits to the base of the flagstones and 

 grits of the Berwyns, and which at the time were considered to be 

 older than the Silurian rocks of Murchison.' 



The subsequent researches of Sedgwick enabled him to fix the 

 boundary-line of the Cambrian and Silurian rocks at the base of the 

 May Hill Series, a line which the further observations of geologists 

 have tended to confirm, as one well marked by a palaeontological, 

 and also, in many instances, by a physical break of large extent. 

 Unfortunately, Sedgwick's Upper Cambrian was ultimately found to 

 possess the fossils of Murchison's Lower Silurian. Murchison, 

 however, who had included the Caradoc and Llandeilo beds in his 

 Silurian system, but had misplaced them in his typical section, did 

 not concede these strata to the Cambrian ; and finding that his 

 system had no definite base on which to rest, took in from time to 

 time group after group of the underlying series, and had to prove 

 at each step that as yet no break had been found in the series, 

 until at length he annexed part of the lowest Cambrian.' Hence 

 arose a painful controversy. And diff"erent classifications have 

 been adopted by geologists, some upholding that of Sedgwick ; 

 some (including the Directors of the Geological Survey in their 

 publications) adopting that of Murchison ; while others again have 

 endeavoured to effect a compromise, and have drawn the line 

 between Cambrian and Silurian, at various horizons, about midway 

 in the debateable ground. Again, some have used the term 

 Cambro-Silurian for the Upper Cambrian, while Prof. C. Lapworth 

 has proposed the term Ordovician for the same division, a term 

 which meets with increasing favour, and appears well fitted to cut 

 the Gordian knot ; for although there is no unconformity with the 

 beds below, the Ordovician group contains a new and distinct 

 fauna.* 



And here it may be mentioned that Joachim Barrande, labouring amongst the 

 older rocks of Bohemia, identified not only the Upper and Lower Silurian rocl<s of 

 Murchison, but an earHer set of strata, containing a distinct fauna. To this "■ Fnst 

 fatdta" lie applied the name "Primordial zone," and unhappily grouped it as 

 Silurian, using that term for all the fossiliferous strata older than Devonian. The 

 fossils of the Lower Silurian were grouped as the '■^ Second fauna, " a.x\d \\\o?.q oi 

 the Upper Silurian as the " Third fauna." These faunas in their collective aspect 

 are distinct. 



M. Barrande paid special attention to the subject of " colonies " of fossils. He 

 recognized at certain horizons in Lower Silurian rocks, members of his Upper 

 Silurian fauna. And he concluded that during the Lower Silurian period in 

 Bohemia, certain forms that lived on to Upper Silurian times existed at a distance 



1 Q. J. viii. 149. 



- See Sedgwick and F. M'Coy, Synopsis of the Classification of the British 

 Palaeozoic Rocks; and J. W. Salter, Catalogue of Cambrian and Silurian Fossils, 

 Cambridge. Also T. Sterry Hunt, History of the Names Cambrian and Silurian, 

 G. Mag. 1873, p. 385 ; T. McK. Hughes, Discussion at Meeting of Geol. Soc. 

 December 2, 1874; Rep. Brit. Assoc. 1875 ; Q.J. xxxi. 194; Jukes, Pop. Phys. 

 Geology, p. 212 ; C. Lapworth, G. Mag. 1S79, p. i. 



3 C. Lapworth, G. Mag. 1881, p. 261 ; Hicks, P. Geol. Assoc, vii, 297. 



