MURCHISON ON THE SILURIAN SYSTEM. 181 



that if there be errors in so large and diffuse a work as the ' Silurian 

 System,' I ought not in fairness to be judged in 1852 by errors put 

 forth in 1835-38. How progressive our science is, he has himself 

 shown in several of his memoirs, in which, using the clue afforded by the 

 fossiliferous rocks of the Silurian System, he unravelled and classified 

 the older rocks of North Wales and Cumberland. In justice also he 

 will not, I am sure, ignore what was done by myself and associates in 

 foreign countries, where we traced a "base-line" on a great scale. 

 Ten years have elapsed since I applied that view to Britain, and I 

 claim, therefore, to be judged only by the final and extended Silu- 

 rian System which was promulgated in 1842, and not by every detail 

 in the original work of 1838 ; though I am well pleased to find that 

 its general views have been sustained by the researches of the Govern- 

 ment Surveyors. 



Together with proofs of physical identity, the Naturalists of the 

 Government Survey have satisfied themselves, that the Silurian, 

 though locally divisible into parts and formations, is one Natural 

 History System, and as such they have arranged it ; showing that a 

 very great number of the species of its fossils are common to its 

 lower and upper divisions. I am further distinctly assured, both by 

 their publications and by many recent communications, that eminent 

 palseontologists of foreign countries are of the same opinion; and 

 in proof of it they have adopted the word "Silurian" as applied by 

 myself during the last eleven years, to the lowest known fossil- 

 bearing strata. 



Widely as the Lower Silurian rocks are expanded in North Wales, 

 and interlaminated as they are there with huge igneous masses, they 

 contain no greater number of fossils characteristic of their age, than- 

 beds of only a twentieth part their thickness in some other parts of 

 the world. The Silurian rocks of Norway, for example, as copiously 

 laden with fossils as strata of the same age in any other part of 

 Europe, rise up to the east and west from beneath the Old Red Sand- 

 stone of R-ingerigge, and so occupy the depressions of Christiania and 

 Steensfiord, that both the lowest and uppermost members of the 

 System are repeated in undulations within the space of a mile or two, 

 are perfectly conformable, and utterly inseparable. The accompa- 

 nying section, which T made in the year 1844, fully explains the 

 phsenomena*. 



It therefore follows, that if, when Professor Sedgwick formerly exa- 

 mined the rocks of Cambria, he had ascertained by examination that 

 both the strata and the fossils were really the same as what I de- 

 scribed as Lower Silurian, and that, in consequence, two distinct 



* k rough and imperfect sketch of this important section appeared in the Pro- 

 ceedings of April 30, 1845 (Quart. Journ. Geol. Soc. vol. i. p. 469) ; and an en- 

 larged and more con-ect sketch, taken from * The Geology of Russia in Europe and 

 the Ural,' was inserted in 'Miscellanea' of the second volume of the Quart. Journ. 

 Geol. Soc. (Part II. p. 71). In this position, however, it has escaped notice; 

 and it is here reproduced in illustration of the ahove remarks on the facts relating 

 to the small development of the rich Upper and Lower Siluiian rocks in Norway. 

 — [R.I.M.] 



