i6 



NATURE 



[May 2, 1872 



dello were underlain by the slaty rocks which appear along their 

 north-western border. When, however, they entered the region 

 which had already been exarnined by Sedgwick, and reached the 

 section on the east side of the Berwyns, the fossihferous beds of 

 Meifod were at once pronounced by Mnrchison to be typical 

 Caradoc, while others in the vicinity were regarded as Llandeilo. 

 The beds of Meifod had, on palreontological grounds, been by 

 Sedgwick identified with those of Glyn Ceirog, which are seen to 

 be immediately overlain by Wenlock rocks. These determina- 

 tions of Murchison were, as Sedgwick tells us, accepted by him 

 with great reluctance, inasmuch as they involved the upper part 

 of his Cambrian .section in most perplexing difficulties. Wlien, 

 however, they crossed together the Berwyn chain to Bala, the 

 limestones in this locality were found to contain fossils nearly 

 agreeing with those of the so-called Caradoc of Meifod. The 

 examination of the section here presented showed, however, tliat 

 these limestones are overlain by a series of several thousand feet 

 of strata bearing no resen.blance, either in fo-isils or in physical 

 characters, to the Wenlock for.nation which overlies theCa'ado- 

 beds of Glyn Ceirog. Tiiis series was, therefore, by Murchison 

 supp ised to be ident'cil with the rocks which, in .South Wales 

 he had placed beneith the Llandeif), and he expresslj' declared 

 that the Bala group cmld not be brought within the limits of 

 his Silurian system. It may here be ailed that in 1842 Sedg- 

 wick re-e-xamined this rj-gion, accomjianied by that skilled 

 palaeontologist, .Salter, confirming the accuracy of his former sec- 

 tions, and showing moreover by the evidence of fossils that the 

 beds of Meifod, Glyn Ceirog. and Bala, are very nearly on one 

 parallel. Y^t, with the evidence of the fo-sils before him, Mur- 

 chison, in 1S34. placed the first two in his Silurian system, and 

 the last deep down in the Upper Cambrian ; and c msequently 

 was aware ihat on pah"eontological grounds it was i'npossitile to 

 separate the lower portion of his Silurian system from the Upper 

 Cambrian of Sedgwick. (These names are here used for cmve- 

 nience, although we are speaking of a time when they had not 

 been applied to designate the rocks in question. ) 



This fact was repeatedly insisted upon by Sedgwick, who, in 

 the Syllabus of his Cambridge lectures, published very early in 

 1837, enumerated the principal genera and species of Upper 

 Cambrian fossils, many of which were by him declared to be the 

 same with those of the Lower Silurian rocks of Murchison. 

 Again, in enumerating in the same Syllabus the chiracterisiic 

 species of the Bala limestone, it is added by Sedgwick : " all of 

 which are common to the Lower Silurian system." This was 

 again ins sted upon by him in 1S38 and 184!. ( Pr ic. Oeok Soc. 

 ii. 679; iii. 548.) It was not until 1S40 that Bowman an- 

 nounced the same conclusion, which was reiter ited by Shirpe 

 in 1842. (Ramsay, Mem. Geol Sur, iii., part 2, p. 6.) 



In 1839 ^[^rchison published his " Silurian System," dedicated 

 to Sedgvvick, a magnificent work in t'A-o volumes quarto, with a 

 separate map, numerous s;ctions, and figures of fossils. The 

 succession of the Silurian rocks, as there given, was precisely 

 that already set forth by the author in 1834. and again in 1835 ; 

 being, ia descending order, Ludlow and Wenlick, constituting 

 the Upper Silurian, and Caradoc and Llandeilo (including the 

 I.,ower Llandeilo beds or Stiper-stones) the Lower Silurian. 

 These are underl.ain by the Cam >rian rock'^, into which the Llan- 

 deilo was said to (jffer a tran.sition marketl by beds of pass.age. 

 Murchiso 1 in fact declared that it was impo sible to draw a ly 

 line of separation, either litholo.,'ica', zool igical, or stratiiirajjlii- 

 cal, between the base of the Silurian beds (Llandeilo) and the 

 upper portion of the Cambrian, the whole firming, according to 

 him, in Caermarthenshire. one continuous and conformible series 

 from the Cambrian to the Ludlow. ("Silurian System," pp. 

 256, 3$8.) By Cambrian in this connection we are to und-rstaiid 

 only the Upper Cambrian or Bala group of Sedgwick, as appears 

 from the express statement of Murchison, who alludes to the 

 Cambri.an of .Sedgwick as including all the older slaty rocks of 

 Wales, and as divided into three groups, but proceeds to say 

 that in his present w irk (th- ".SiKinan System ") he shall notice 

 only th''; highest of these three. 



Since January 1834, when Murchison first announced the 

 stratigraphicil rel.Uioiis of the lower divi:-ion of what he after- 

 wards called the Silurian system, the aspect of the case had 

 materially changed. This division was no longer underlain, both 

 to the eist in Shropshire and to the west in Wales, by a great 

 unfossili emus serie.s. Hi, obs ■ v itions in the vicinity of the 

 Berwyn hills wiih .Sedg.vick in 1S34, and the .subsequently pub- 

 lished statements of ttie latter had shown, that t lis supposed of ler 

 series was not without fossils ; but on the contrary, in Norch 

 Wales, at least, held a fauna identical with that characterising 



the Lower Silurian. Hence the assertion of Murchison in his 

 " Silurian System," in 1839, that it was not possible to draw any 

 line of demarcation between them. The position was very 

 embarrassing to the author of the "Silurian Systan," and for 

 the moment, not less so to the discoverer of the Upper Camlirian 

 series. Meanwhile, the latter, as we have seen, in 1842 re- 

 examined with Salter his Upper Cambrian sections in North 

 Wales, and satisfied himself of the correctness, both structurally 

 and palsiontologically, of his former determinations. Murchison, 

 in his Anniversary A Idress a^ President of the Geological Society 

 in 1S42, after recounting, as we have already done, the history of 

 the naming by Sedgwick in 1839 of the Cambrian series, which 

 Murchison supposed to underlie his Silurian system, proceeded 

 as follows : — " Nothing precise was then known of the organic 

 contents of this lower or Cambrian system, except that some of 

 the fossils contained in its upper members in certain prominent 

 l-jcalities were published Lower Silurian species. Meanwhile, 

 by adopting the word Cambrian, my friend and my~elf were 

 certain that whatever might prove to be i's zoological distinctions, 

 this grea' system of slaiy rocks being evidently inferior to those 

 zones which had been worked out as Silurian types, no ambi- 

 guity could hereafter arise. ... In regard, however, to a 

 descending zoological order, it still remained to be proved 

 whether there was any type of fossils in the mass of the Cam- 

 brian rocks different from tho.e of the Lower Silurian series. If 

 the appeal to nature should l>e answered in the negative, then it 

 was clear that the Lower .Silurian type must be considered the 

 true base of what I had nimed the protozoic rocks ; but if 

 characteristic new forms were discovered, then would the Cam- 

 brian rocks, whose place was so well established in the descend- 

 ing series, have also their own fiuna, and the palaeozoic base 

 would neces arily be removed to a lower horizon." If the first 

 of these alternatives should be established, or in other words, 

 if the fauna of the Cambrian rocks was found to be identical 

 with that of the Lower Silurian, then, in the author's language, 

 " the term Cambrian must cease to be used in zoological classifi- 

 cation, it being, in that sense, synonymous with Lower Silurian." 

 That such was the result of pal.tontological inquiry, Murchison 

 proceeded to show, by repeating the announcements already 

 made by Sedgwick in 1837 and 1S3S, that the collections made 

 by the latter from the great series of fossiliferous strata in the 

 Berwvns, from Bala, from Snowden, and other Cambrian tracts, 

 were identical wiih the Lower Silurian forms. These strata, it 

 was siid, contain throughout " the same forms of 0?'////j which 

 tvpily the Lower .Si urian rocks. " It was further declared by 

 Murchison in this address that researches in Germany, Belgium, 

 and Rus,ia led to tlie conclusion that the "fossiliferous strata 

 characterised by Lower Siluri.an Orthida; are the oldest beds in 

 which organic life has been de'ected." (Croc. Geol. Soc. iii. 

 641, &c. ) The Orihids here referred to are, according to Salter, 

 Ortkis calll^rainma, Dalm, and its varieties. (Mem. Geol. 

 Survey iii, part 2, 335-337.) 



iVIeanwhile Sedgwick's views and position began to be misre- 

 presented. In 1842 Mr. Sharpe, after calling attention to the 

 fact that the fossils of the Bala limestone were, as .Sedgwick had 

 long before shown, identical with those of Murchis -n's Lower 

 .Silurian, declared that Sedgwick had placed the Upper Cam- 

 brian, in which the Bala beds were included, beneath the 

 Silurian, and that this determination had b. en adopted by Mur- 

 chison on Selgwick's authirity. (Proc. Geol. Soc. iv. 10.) This 

 statement Murchison suffered to pass uncorrected in a compli- 

 mentary review of Sharpe's paper in his next annml address 

 (1843.) In his " Slluria," 1st edition, p. 25 (1854), he speaks of 

 the term Cambrian as applied (in 1835) by Se 'g.vick and himself 

 "to a vast succession of /Itssili/hoiis strata containing unde- 

 scrlbed fossils, the whole of which were supposed to rise up from 

 beneath well-known Silurian rocks. The Government geologists 

 hive shown that this supposed order of superposition was 

 erroneous," &c. The italics are the auth .r's. Such language, 

 coupled with Mr. Sharpe's assertion noticed above, helped to fix 

 upon .Sedgwick the responsibility of .Vlurchison's error. Although 

 the historical sketch which precedes clearly shows the real posi- 

 tion of Sedgwick in the matter, we m.ay quote further his own 

 words : — " I have often spoken of the great Upper Cambrian 

 group of North Wales as inferior to the .Silurian system, . . 

 on the sole authority of the Lower .Silurian sections, and the 

 author's many times repeated explanations of them before they 

 were publislied. So great was my confidence in his work, that I 

 received it as perfectly established trutii that his order of super- 

 position was unassailable. ... I asserted again and again 

 that the Bala limestone was near the base of the so-called Upper 



