286 THE CANADIAN NATURALIST. [Vol. vi. 



upon by him in 1838 and 1841. [Proc. Geol. Soc. II, 679; III, 

 548.] It was not until 1840 that Bowman announced the 

 same conclusion, which was reiterated by Sharpe in 1842. [Ram- 

 say, Mem. Geol. Sur. Ill, part 2, page 6.] 



In 1839, Murchison published his Silurian System, dedicated 

 to Sedgwick, a magnificent work in two volumes quarto, with a 

 separate map, numerous sections 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, in descending order, Ludlow and Wenlock, constituting 

 the Upper Silurian, and Caradoc and Llandeilo (including the 

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

 These are underlaid by the Cambrian rocks, into which the Llan- 

 deilo was said to ofier a transition marked by beds of passage. 

 Murchison, in fact, declared that it was impossible to draw any 

 line of separation either lithological, zoological or stratigraphical 

 between the base of the Silurian beds (Llandeilo) and the upper 

 portion of the Cambrian, — the whole forming, according to him, 

 in Caermarthenshire, one continuous and conformable series from 

 the Cambrian to the Ludlow. [Silurian System, pages 256, 358.] 

 By Cambrian in this connection we are to understand only the 

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

 express statement of Murchison, who alludes to the Cambrian 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 

 work (the Silurian System) he shall notice only the highest of 

 these three. 



Since January, 1834, when Murchison first announced the 

 stratigraphical relations of the lower division of what he after- 

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

 materially changed. This divibion was no longer underlaid, both 

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

 unfossiliferous series. His observations in the vicinity of the 

 Berwyn hills with Sedgwick in 1834, and the subsequently pub- 

 lished statements of the latter had shown, that this supposed older 

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

 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 em- 

 barrassing to the author of the Siliman System, and for the mo- 



