296 A. J. Julies-Browne — On Eoch- Classification. 



■which Dr. Blanford recommends, and especially against the artificial 

 plan of allowing only three systems to each great era of time. Such 

 a plan is certain to give rise to erroneous impressions, and strikes 

 me as an application of mathematics to geology which is not 

 likely to yield useful results. What would Historians think of an 

 attempt to divide English History into three unequal eras, each sub- 

 divided into three unequal periods, with every reign or chapter 

 treated in three parts ? Is there such magic in the number three that 

 a tripartite division of the geological record is calculated to afford us 

 a clearer conception of its contents ? Even the three cardinal divi- 

 sions are hardly defensible on palgeontological grounds, though they 

 are convenient for some purposes. A primary division into Palceozoic 

 and Neozoic, with five or six systems in each, would be far more 

 scientific. 



I adopt Prof. Lapworth's name Ordovician for the system of the 

 second fauna, as the only practicable way out of the Sedgwick and 

 Murchison controversy, and certainly regard the Cambrian, Ordo- 

 vician, and Silurian as systems equivalent in palaeontological value 

 to Devonian and Carboniferous. I think, however, the nomenclature 

 of the Ordovician series stands in need of improvement; Lower, 

 Middle, and Upper would, perhaps, be better than retaining the old 

 names of Arenig, Llandeilo, and Bala for the primary divisions. 



In the case of the Silurian system a different nomenclature must 

 be adopted because of the confusion which would arise from the 

 use of 'Lower' Silurian. Prof. Lapworth's name of Valenttan may 

 be adopted for the Llandoveries, Salopian may do for the Middle 

 series, but Doiontonian, which has been used for the Upper series, is 

 so eminently unclassical that it will hardly pass muster. A new 

 name seems, therefore, to be required, and I venture to propose 

 Clunian from Clun Forest, in Shropshire, where these uppermost 

 Silurians and the Tilestones are largely developed (see Sheet 30 

 of the Horizontal Sections of the Geological Survey, and Jukes' 

 Manual of Geology, 2nd ed. p. 481). For the Devonian system the 

 marine series must clearly be adopted as the type, but it is possible 

 that some of the Upper Devonian and Upper O.R.S. may have to 

 be transferred to the Carboniferous system. 



As regards the Carboniferous system, I find there are weighty 

 objections to Prof. Hull's proposals to create a Middle series. The 

 Yoredales are so essentially a part of the Carboniferous Limestone 

 series, that they ought not to be separated from it, while the Millstone 

 Grit is similarly linked to the Coal-measures. Moreover, Prof. Green 

 has shown that there is a well-marked line at the base of the Mill- 

 stone Grit, so that the old division of the system into an Upper and 

 Lower appears more true to nature than a triple series would be. 



Whether the Dyas (Permian) is entitled to rank as a separate 

 system is very doubtful. The conditions under which it was formed 

 appear to have enabled a portion of the Carboniferous fauna to 

 perpetuate their existence in the European area while Mesozoic life 

 was being rapidly developed elsewhere. I doubt, therefore, whether 

 we can in this instance take Paleeontology as a guide, and think it 



