Silurian Discussion. Ill 



1832, or to appeal to what he communicated verbally in the latter 

 year respecting a part of North Wales, the only printed record of 

 which is comprised in about twenty lines of the first volume of the 

 Transactions of the British Association, 



The first methodical and digested view of a sedimentary succes- 

 sion beneath the known and fixed horizon of the old red-sandstone, 

 was presented by myself to the Geological Society in 1834,* as 

 the result of memoirs of 1831, 1832, and 1833. The four forma- 

 tions described then as " fossiliferous greywacke," were, in the 

 year 1835, named the Silurian System, the two superior (Ludlow 

 and Wenlock) being termed Upper, the two inferior (Caradoc and 

 Llandeilo) Lower Silurian, and each being characterised by its 

 fossils. 



In 1836 the word Cambrian was first used, Professor Sedgwick 

 affirming that the slaty rocks which he so termed, and which laid 

 to the west of the Silurian region, were all of them inferior to the 

 strata of my system. This inferiority of position has proved to be 

 a fundamental misconception, as now demonstrated by the physical 

 researches of the Government geological surveyors. In their 

 hands the Cambria of Sedgwick, which was undefined and unknown 

 through any publication of its fossils, has proved to be identical 

 in age with the original published Siluria of Murchison. 



In 1838, when the detailed descriptions of the composition of 

 the Silurian System were published, I spoke of the line of demar- 

 cation on my map, as being provisionally set up between the 

 Silurian rocks with which I was well acquainted, and a Cambrian 

 series of which I was ignorant. But the latter being said to be 

 vastly inferior to all the strata I described, I naturally believed it 

 would prove, in the hands of my friend, to contain a distinct sys- 

 tem of former life. Strata, identified by their fossils and infra- 

 position to a known horizon, were the bases of my classification and 

 nomenclature ; and no other idea ever crossed my mind than that 

 the Cambrian could alone be established as a system, by having a 

 fauna different from my own, and by being inferior to it. Various 

 passages in my original works clearly expose this view. 



My friend says, that in 1843 I shifted my ground, and put a 

 new meaning upon my views, in order to bring them into confor- 



! mity with a new map founded on a new scheme of nomenclature. 

 The recorded facts, he must forgive me for saying, are quite op- 

 posed to this assertion, and are indeed well known to practical 

 geologists. The little geological map of England and Wales, 

 published by me in 1843, at the request of the Society for the 

 Diffusion of Useful Knowledge, was not issued " rashly" but after 



i much deliberation and examination. 



* Proceedings of the Geological Society, vol. ii. p. 13. 



