388 Prof. T. 8ternj Hunt — On Cambrian and Silurian. 



Meanwhile, to go back to 1834, we find that after Murchison had, 

 in his communication to the Geological Society, defined the relation 

 of his Llandeilo formation to the underlying slaty series, but before 

 the names of Silurian and Cambrian had been given to these re- 

 spectively, Sedgwick and Murchison visited together the principal 

 sections of these rocks from Caermarthenshire to Denbighshire. 

 The greater part of this region was then unknown to Sedgwick, 

 but had been already studied by Murchison, who interpreted the 

 sections to his companion in conformity with the scheme already 

 given ; according to which the beds of the Llandeilo were underlaid 

 by the slaty rocks which appear along their north-western border. 

 When, however, they entered the region which had already been 

 examined by Sedgwick, and reached the section on the east side of 

 the Berwyns, the fossiliferous beds of Meifod were at once pro- 

 nounced by Murchison to be typical Caradoc, while others in the 

 vicinity were regarded as Llandeilo. The beds of Meifod had, on 

 palsBontological grounds, been by Sedgwick identified with those of 

 Glyn Ceirog, which are seen to be immediately overlaid by Wenlock 

 rocks. These determinations of Murchison were, as Sedgwick tells 

 us, accepted by him with great reluctance, inasmuch as they in- 

 volved the upper part of his Cambrian section in most perplexing 

 difficulties. When, 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, that 

 these limestones are overlaid by a series of several thousand feet of 

 strata bearing no resemblance either in fossils or in physical character 

 to the Wenlock formation which overlies the Caradoc beds of Glyn 

 Ceirog. This series was, therefore, by Murchison supposed to be 

 identical with the rooks which in South Wales he had placed be- 

 neath the Llandeilo, and he expressly declared that the Bala group 

 could not be brought within the limits of his Silurian system. It 

 may here be added that in 1842 Sedgwick re-examined this region, 

 accompanied by that skilled palaeontologist, Salter, confirming the 

 accuracy of his former sections, and showing moreover, by the evi- 

 dence of fossils, that the beds of Meifod, Glyn Ceirog and Bala are 

 very nearly on one parallel. Yet, with the evidence of the fossils 

 before him, Murchison, in 1834, placed the first two in his Silurian 

 system, and the last deep down in the Upper Cambrian ; and conse- 

 quently was aware that on palaeontological grounds it was impossible 

 to separate the lower portion of his Silurian system from the Upper 

 Cambrian of Sedgwick. (These names are here used for convenience, 

 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 tlie same with 

 those of the Lower Silurian rocks of Murcliison. Again, in enume- 

 rating in the same Syllabus the characteristic species of the Bala 

 limestone, it is added by Sedgwick: "all of which are common to 



