422 



NATURE 



\March 6, 1890 



the sections from the top of the Berwyns to. Bala. 

 Murchison concluded, after his brief examination, and 

 told Sedgwick, that the Bala group could not be brought 

 within the limits of his system. He says : " I believed it 

 it to plunge under the true Llandeilo flags with Asaphus 

 Buchii, which I had recognized on the east flank of that 

 chain," " Not seeing, on that hurried visit, any of the 

 characteristic Llandeilo Trilobites in the Bala limestone, 

 I did not then identify that rock with the Llandeilo flags, 

 as has since been done by the Government surveyors " 

 (O. J. G. Soc, viii. 175). 



~In 1835, the terms "Silurian" and "Cambrian" first 

 appear in geological literature. Murchison named his 

 system the " Silurian " in an article in the Philosophical 

 Magazine for July of that year, and at the same time 

 defined the two grand subdivisions of the system : (I.) 

 the Upper Silurian, or the Ludlow and Wenlock beds ; 

 and (11.) the lower Silurian, or the Caradoc and Llandeilo 

 beds {Phil. Mag., vii. 46, July 1835). 



During the next month, August, the fourth meeting of 

 the British Association was held at Edinburgh, and in 

 the Report of the meeting (Brit. Assoc, v., August 1835), 

 the two terms, " Silurian " and " Cambrian," are united 

 in the title of a communication "by Prof Sedgwick and 

 R. I. Murchison," the title reading, " On the Silurian and 

 Cambrian Systems, exhibiting the order in which the 

 older sedimentry strata succeed each other in England 

 and Wales." Murchison, after explaining his several 

 subdivisions, said that " in South Wales" he had "traced 

 many distinct passages from the lowest member of the 

 " Silurian system " into the underlying slaty rocks now 

 named by Prof. Sedgwick the Upper Cambrian." Sedg- 

 wick spoke of his " Upper Cambrian group " as including 

 the greater part of the chain of the Berwyns, where, he 

 said, " it is connected with the Llandeilo flags of the 

 Silurian and expanded through a considerable part of 

 South Wales"; the "Middle Cambrian group" as 

 " comprising the higher mountains of Caernarvonshire 

 and Merionethshire"; the "Lower Cambrian group" as 

 occupying the south-west coast of Caernarvonshire, and 

 consisting of chlorite and mica schists, and some serpen- 

 tine and granular limestone ; and finally, he " explained 

 the mode of connecting Mr. Murchison's researches with 

 his own so as to form one general system." 



Thus, in four years Murchison had developed the true 

 system in the rocks he was studying ; and Sedgwick like- 

 wise had reached what appeared to be a natural grouping 

 of the rocks of his complicated area. Further, in a united 

 paper, or papers presented together, they had announced 

 the names Silurian and Cambrian, and expressed their 

 mutual satisfaction with the defined limits. Neither was 

 yet aware of the unfortunate mischief-involving fact that 

 the two were overlapping series. 



It is well here to note that tJie term " Cambrian " ante- 

 dates " Taconic" of Enwions by seven year^j and also 

 that Emmons did not know — any more than Sedgwick 

 with regard to the Cambrian — that his system of rocks 

 was in part Lower Silurian, and of Llandeilo and Caradoc 

 age. 



In May of 1 838, nearly three years later, Sedgwick 

 presented his first detailed memoir on North Wales and 

 the Cambrian rocks to the Geological Society.^ Without 

 referring to the characteristic fossils, he divides the rocks 

 below the Old Red Sandstone, beginning below, into (I.) 

 the Primary Stratified Groups, including gneiss, mica- 

 schist, and the Skiddaw slates, giving the provisional 

 name of " Protozoic " for the series should it prove to be 

 fossiliferous, and (II.) the Palaeozoic Series ; the latter 

 including (i) the Lower Cambrian (answering to Middle 

 Cambrian of the paper of 1835), (2) the Upper Cambrian, 

 and (3) the " Silurian,'' or the series so called by Muithi. 



^ An abstract appeared in the Proc. Geo]. Soc, ii. 675, 1838. A continua- 

 tion of the paper appeared in i8ii, ibid., iii. 541. See also Q. J. Geol. Soc, 

 viii., 1852. 



son. Without a report on the fossils, no comparison was 

 possible at that time with Murchison's Silurian series. 

 Yet Sedgwick goes so far as to say that the " Upper 

 Cambrian," which "commences with the fossiliferous 

 beds of Bala, and includes all the higher portions of the 

 Berwyns and all the slate-rocks of South Wales which 

 are below the Silurian System," "appears to pass by 

 insensible gradation into the lower division of the Upper 

 System (the Caradoc Sandstone) ; " and that " many of 

 the fossils are identical in species with those of the 

 Silurian System." ' Respecting the Silurian System he 

 refers to the abstracts of Mr. Murchison's papers and 

 " his forthcoming work." 



The Protozoic division included the " Highlands of 

 Scotland, the crystalline schists of Anglesea, and the 

 south-west coast of Caernarvonshire." It is added : 

 " The series is generally without organic remains ; but 

 should organic remains appear unequivocally in any part 

 of this class they may be described as the Protozoic 

 System." 



In the later part of the same year, 1838, Murchison's 

 " Silurian System " was published ^ — a quarto volume of 

 800 pages, with twenty- seven plates of fossils, and nine 

 folded plates of stratigraphical sections, besides many 

 plates in the text— the outcome of his eight years of 

 work. Five hundred pages are devoted to the Silurian 

 System. 



The dedication is as follows : — 



" To you, my dear Sedgwick, a large portion of whose 

 life has been devoted to the arduous study of the older 

 British rocks, I dedicate this work. 



" Having explored with you many a tract, both at home 

 and abroad, I beg you to accept this offering as a memorial 

 of friendship, and of the high sense I entertain of the value 

 of your labours." 



Through Murchison's investigations here recorded, as 

 he remarks in his introduction with reasonable satisfac- 

 tion, "a complete succession of fossiliferous strata is 

 interpolated between the Old Red Sandstone and the 

 oldest slaty rocks." He observes as follows of Sedg- 

 wick : — " In speaking of the labours of my friend, I may 

 truly say, that he not only shed an entirely new light on 

 the crystalline arrangement or slaty cleavage of the North 

 Welsh mountains, but also overcame what to rnost men 

 would have proved insurmountable difficulties in deter- 

 mining the order and relations of these very ancient 

 strata amid scenes of vast dislocation. He further made 

 several traverses across the region in which I was em- 

 ployed ; and, sanctioning the arrangement I had adopted, 

 he not only gave me confidence in its accuracy, but 

 enhanced the value of my work by enabling me to unite 

 it with his own ; and thus have our joint exertions led to 

 a general view of the sequence of the older fossiliferous 

 deposits." In accordance with these statements many of 

 the descriptions and the very numerous sections represent 

 the Cambrian rocks lying beneath the Silurian— though 

 necessarily with incorrect details, since neither Murchi- 

 son nor Sedgwick had then any appreciation of the 

 actual connection between the so-called Cambrian and 

 Silurian. 



The Silurian System, as here set forth, is essentially 

 that of Murchison's earlier paper of 1835 ; and through 

 the work, as each region is taken up, the rocks of the 

 Upper and Lower divisions, and their several subdivisions, 

 are described in order, with a mention of the character- 

 istic fossils. As to the relations of the two grand divi- 

 sions, he says that, " although two or three species of 



' Of these fossils, he had mentioned '' BelleroJ>hon bilobatits, Frodiida 

 sericea, and several species of Orthis" as occurring in the Bala limestone, 

 " all of which are common to the Lower Silurian System, in a syllabus oi 

 his Cambridge lectures, published in 1837. ■ , . a „ 



- Murchison's " Silurian System " bears on its title-page the date i8:,9. 

 He states m the Q.J. Geol. Soc, viii. 177, 1852, that the work was really 

 issued in 1838. The fossil fishes of the volume were described by Agassi/, 

 the Trilobites by Murchison, and the rest of the species by Sowerby. 



