306 THE CANADIAN NATURALIST. * [Yol. vi. 



fauna, even though Barrande and the government surveyors 

 shouki unite in calling it Primordial Silurian. 



He however chose the opposite course, and now attempted to 

 claim for the Silurian system the whole of the Middle Cambrian 

 or Festiniog group of Sedgwick, including the Tremadoc slates 

 and the Lingula-flags. The grounds of this assumption, as set 

 forth in the successive editions of Siluria from 1854 to 1867, and 

 in various memoirs, may be included under three heads : first 

 that the Lingula-flags have been found to exist in some parts of 

 his original Silurian region ; second, that no clearly-defined base 

 had been assigned by him to his so-called system ; and third, that 

 there are no means of drawing a line of demarkation between 

 these Middle Cambrian formations and the overlying Llandeilo. 



With regard to the first of these reasons, it is to be said that 

 the only known representatives of the Lingula-flags in the region 

 described by Murchison in his Silurian System are the black 

 slates of Malvern ; and some scanty outliers which, in Shropshire, 

 lie between the old Longmynd rocks and the base of the Stiper* 

 Stones. The former were then (as has already been shown) sup- 

 posed by him to belong to the Llandeilo, or rather to the passage- 

 beds between the Llandeilo and Cambrian (Bala) ; while with 

 regard to the latter, Ramsay expressly tells us that they were not 

 originally classed with the Silurian, but have since been included 

 in it. [Mem. Geol. Sur. Ill, part 2, page 9 ; and 242, foot-note.] 



The Llandeilo beds were by Murchison distinctly stated to be 

 the base of the Silurian system [Sil. Sys. 222.] ; and it was far- 

 ther declared by him that in Shropshire; (unlike Caermartheo- 

 shire,) " there is no p .ssage from the Cambrian to the Silurian 

 strata," but a hiatus, marked by disturbances which excluded the 

 passage-beds, and caused the Lower Silurian to rest unconform- 

 ably upon the Longmynd rocks. [Ibid, 256; and plates 31, sec- 

 tions 3 and 6; 32, section 4.] But in Siluria [1st. ed. 47] the 

 two are stated to be conformable; and in the subsequent sections 

 of this region, made by Aveline, and published by the Geological 

 Survey, the evidences of this want of conformity do not appear^ 

 Murchison at that time confounded the rocks of the Longmynd 

 with the Cambrian (Bala) beds of Caermarthenshire and Brecon, 

 [Sil. Sys. 416.] Hence it was that he gave the name of Cam- 

 brian to the former; and this mistake, moreover, led him to place 

 the Cambrian of Caermarthenshire beneath the Llandeilo. It is 

 clear that if he claimed no well-defined base to the Llandeilo 



