506 Prof. T. Sterry Hunt — On Cambrian and Silurian. 



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 be- 

 tween the old Longmynd rocks and the base of the Stiper- stones. 

 The former were then (as has already been shown) supposed 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, 

 Eamsay expressly tells us that they were not originally classed with 

 the Silurian, but have since been included in it. (Mem. Geol. Surv., 

 vol. iii. 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. Syst. p. 222) ; and it was farther 

 declared by him that in Shropshire (unlike Caermarthenshire) 

 "there is no passage 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 unconformably upon the 

 Longmynd rocks. {Ibid. p. 256 ; and plates 31, sections 3 and 6 ; 

 32, section 4.) But in Siluria (1st ed. p. 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. Syst. p. 416.) Hence 

 it was that he gave the name of Cambrian to the former; and this 

 mistake, moreover, led him to place the Cambrian of Caermarthen- 

 shire beneath the Llandeilo. It is clear that if he claimed no well- 

 defined base to the Llandeilo rocks in this latter (their typical 

 region), it was because he saw them passing into the overlying 

 Bala beds. There was, in the error by which he placed beloio the 

 Llandeilo, strata which were really above them, no ground whatever 

 for afterwards including in his Silurian system, as a downward con- 

 tinuation of the Llandeilo rocks (which are the basal portion of the 

 Bala group), the whole of the Ffestiniog group of Sedgwick ; whose 

 infra-position to the Bala had been shown by the latter long before 

 it was known to be fossiliferous. 



It was, however, claimed by Murchison that no line of separation 

 can be drawn between these two groups. The results of Eamsay 

 and of Salter, as set forth in the address of the former before the 

 Geological Society in 1863, and more fully in the Memoirs of the 

 Geological Survey (vol. iii. part 2) published in 1866, with a preface 

 by himself, as the Director of the Survey, are completely ignored by 

 Murchison. The reader familiar with these results, of which we 

 have given a summary, finds with surprise that in the last edition of 

 Siluria, that of 1867, they are noticed in part, but only to be re- 

 pudiated. In the five pages of text which are there given to this 

 great Middle Cambrian division, we are told that the distinction 

 between the Lower Tremadoc and the Lingula-flags " is difficult to 

 be drawn," and that the Upper Tremadoc slate passes into and fonns 

 the lower part of the Llandeilo, " into which it graduates confor- 



