1 



424 



NA TURE 



[March 6, 1890 



In December a paper was presented by Sedgwick to 

 the Geological Society, on " The Fossiliferous Slates 

 of North Wales, Cumberland, Westmoreland, and Lanca- 

 shire " (Q. J. Geol. Soc, iii. 133, December 1846), which 

 contains a protest against the downward extension of the 

 Silurian so as to include the Cambrian. It is excellent 

 in spirit and fair in argument. Many new facts are given 

 respecting sections of the rocks in South Wales and North 

 Wales, in some of which occur the Lingula flags, and 

 characteristic fossils are mentioned. In describing some 

 South Wales sections, Sedgwick uses the term " Cambro- 

 Silurian " to include, beginning below: (i) " conglomerates 

 and slates, (2) Lower Llandeilo flags, (3) slates and grits 

 (Caradoc sandstone of Noeth Grug, &c.), (4) Upper 

 Llandeilo flag, passing by insensible gradations into Wen- 

 lock shale." The Cambrian series is made to include : 

 (i) the Festiniog or Tremadoc group ; (2) roofing-slates, 

 &c., the " Snowdonian group," fossiliferous in Snowdon, 

 &c. ; (3) the Bala group; andthen(4)"theCambro-Silurian 

 group," comprising " the lower fossiliferous rocks east of 

 the Berwyns between the Dee and the Severn — the Cara- 

 doc sandstone of the typical country of Siluria — and the 

 Llandeilo flags of South Wales, along with certain asso- 

 ciated slates, flags, and grits." The extension of the 

 term Silurian down to the Lingula flags, or beyond, is 

 opposed, because the beds below the Llandeilo are not 

 part of the Silurian system ; the term Silurian [derived 

 from the Silures of South-East Wales and the adjoining 

 part of England] is not geographically applicable to the 

 Cambrian rocks ; and because the only beds in North 

 Wales closely comparable " with the Llandeilo flags are 

 at the top of the whole Cambrian series." This last 

 reason later lost its value when it was proved, as Sedg- 

 wick recognized years afterward, that Murchison's Llan- 

 deilo flags were really older than Sedgwick's Bala rocks. 



Sedgwick's paper was followed, on January 6, with one 

 by Murchison (O. J. Geol. Soc, iii. 165, January 1847) 

 objecting to this absorption of the Lower Silurian, and 

 reiterating his remark of 1843 that the fossiliferous Cam- 

 brian beds were Lower Silurian in their fossils, and 

 arguing, thence, for the absorption of the Cambrian, to 

 this extent, by the Silurian. Having, eight years before, 

 in his great work on the " Silurian System," described 

 the Lower Silurian groups with so much detail, and 

 with limits well defined by sections and by long lists of 

 fossils, over a hundred species in all, many of them 

 figured as well as described, and having thus added a 

 long systematized range of rocks to the lower part of the 

 Palaeozoic series, he was naturally unwilling to give up the 

 name of Lower Silurian for that of Upper Cambrian or 

 Cambro- Silurian. Moreover, the term " Silurian," with 

 the two subdivisions of the system, the Upper and Lower, 

 had gone the world over, having been accepted by geo- 

 logists of all lands as soon as proposed, become affixed 

 to the rocks to which they belonged, and put into use in 

 memoirs, maps, and geological treatises. 



In 1852, the controversy, begun by encroachments, not 

 intended on either part, reached its height. Sedgwick's 

 earnest presentation of the case (Q. J. Geol. Soc, viii. 

 152), and appeal before the Geological Society in 

 P^ebruary of that year — making the latter part of a 

 memoir by him on the " Classification and Nomen- 

 clature of the Lower Palaeozoic Rocks of England and 

 Wales" — argues, like that of 1846, for the extension of 

 the Cambrian from below upward to include the Bala 

 beds, and thereby also the Llandeilo flags and Caradoc 

 sandstone, although he says, " my friend has published a 

 magnificent series of fossils from the Llandeilo flag- 

 stone." Sedgwick also expresses dissatisfaction with 

 Mr. Warburton's abstract of his paper of June 1843, 

 and with the change made in his map of November 

 1843, but, as shown above, he has no blame for 

 Murchison and little for Mr. Warburton. He also points 

 out some errors in the stratigraphical sections of the 



" Silurian System " — since the pubhcation of which 

 fourteen years had passed. He closes with the words 

 (p. 168) :- 



" I affirm that the name ' Silurian,' given to the great 

 Cambrian series below the Caradoc group, is historically 

 unjust. I claim this great series as my own by the un- 

 doubted right of conquest ; and I continue to give it the 

 name ' Cambrian ' on the right of priority, and, moreover, 

 as the only name yet given to the series that does not 

 involve a geographical contradiction. The name 'Silurian' 

 not merely involves a principle of nomenclature that is at 

 war with the rational logic through which every other 

 Palaeozoic group of England has gained a permanent 

 name, but it also confers the presumed honour of a con- 

 quest over the older rocks of Wales on the part of one 

 who barely touched their outskirts, and mistook his way 

 as soon as he had passed within them. 



" I claim the right of naming the Cambrian rocks be- 

 cause I flinched not from their difficulties, made out their 

 general structure, collected their fossils, and first com- 

 prehended their respective relations to the groups above 

 them and belov/ them, in the great and complicated 

 Palaeozoic sections of North Wales. Nor is this all, — I 

 claim the name Cambrian, in the sense in which I have 

 used it, as a means of establishing a congruous nomencla- 

 ture between the Welsh and the Cumbrian mountains, and 

 bringing their respective groups into a rigid geological 

 comparison ; for the system on which I have for many 

 years been labouring is not partial and one-sided, but 

 general and for all England." 



Sedgwick does not seem to have recognized the fact 

 that Muichison had the same right to extend the Silurian 

 system to the base of the Llandeilo beds, whatever its 

 horizon, that he had to continue the Cambrian to the top' 

 of the Bala beds.^ 



Murchison's reply was made at the meeting of the 

 Geological Society in June (O. J. Geol. Soc, viii. 173, 

 1852). He remarked, with regard to Sedgwick's allusion 

 to the excursion of 1834, that, "if I lost my way in going 

 downward into the region of my friend, it was under his 

 own guidance ; I am answerable only for Silurian and 

 Cambrian rocks described and drawn as such within my 

 own region." 



In his closing remarks Murchison says : — 



" I am now well pleased to find that, with the exceptiork 

 of my old friend, all my geological contemporaries in my 

 own country adhere to the unity of the Silurian System,, 

 and thus sustain its general adoption. 



" No one more regrets than myself that Cambrian 

 should not have proved, what it was formerly supposed to- 

 be, more ancient than the Silurian region, and thus have 

 afforded distinct fossils and a separate system ; but as 

 things which are synonymous cannot have separate names,, 

 there is no doubt that, according to the laws of scientific 

 literature, the term 'Silurian' must be sustained as 

 applied to all the fossiliferous rocks of North Wales. 



" Lastly, let me say to those who do not understand the 

 nature of the social union of the members of the Geo- 

 logical Society, that the controversy which has prevailed 

 between the eloquent Woodwardian Professor and myself 

 has not for a moment interrupted our strong personal 

 friendship. I am indeed confident we shall slide down 

 the hill of life with the same mutual regard which animated 

 us formerly when climbing together many a mountain 

 both at home and abroad." 



Murchison was right in saying that all British geologists 

 were then with him, even in the extension of the name 

 Silurian to the lower fossiliferous Cambrian rocks ; and 

 this was a chief source of irritation to Sedgwick. It was 

 also, with scarcely an exception, true of geologists else- 



' One important fact is pointed out in this paper in a letter from M'Coyr 

 on p. 143 — that the May Hill group, which Murchison had referred t° V*-^ 

 Caradoc series, really belonged by its fossils to the Upper Silurian. T**'* 

 point was the subject of a paper by Sedgwick in the next volume (vol. ix.) ot 

 the Journal of the Geological Society. 



