Prof. T. Sterry Hunt — On Cambrian and Silurian. 393 



4. Wenlock and Ludlow beds ; 5. Old Eed Sandstone ; the order 

 being from north-west to south-east. What then were these fossili- 

 ferous Cambrian beds underlying the Llandeilo and indistinguishable 

 from it ? Sedgwick, with the aid of the Government surveyors, has 

 answered the question in a manner which is well illustrated in his 

 ideal section across the valley of the Towey. The whole of the 

 Bala or Caradoc group rises in undulations to the north-west, while 

 the Llandeilo-flags at its base appear on an anticlinal in the valley, 

 and are succeeded to the south-east by a portion of the Bala, The 

 great mass of this group on the south-east side of the anticlinal is 

 however concealed by the overlapping May Hill sandstone, — the 

 base of the unconformable upper series which includes the Wenlock 

 and Ludlow beds. (Philos. Mag. iv., vol. viii. p. 488.) The 

 section to the south-east, commencing from the Llandeilo-flags on 

 the anticlinal, was made by Murchison the Silurian system, while 

 the great mass of strata on the north-west side of the Llandeilo 

 (which is the complete representative of the Caradoc or Bala beds, 

 j)artial]y concealed on the south-west side) was supposed by him to 

 lie beneath the Llandeilo, and was called Cambrian (the Upper 

 Cambrian of Sedgwick). These rocks, with the Llandeilo at their 

 base, were in fact identical with the Bala group studied by the latter 

 in North Wales, and are now clearly traced through all the inter- 

 mediate distance. This is admitted by Murchison, who says : " The 

 first rectification of this erroneous view was made in 1842, by Prof. 

 Eamsay, who observed that instead of being succeeded by lower 

 rocks to the north and west, the Llandeilo-flags folded over in those 

 directions, and passed under superior strata, charged with fossils 

 which Mr. Salter recognized as well-known types of the Caradoc or 

 Bala beds." (Siluria, 4th ed., p. 57, foot-note.) 



The true order of succession in South Wales was in fact : 1, 

 Llandeilo ; 2, Cambrian ( = Caradoc or Bala) ; 3, Wenlock and 

 Ludlow ; 4, Old Eed Sandstone ; the Caradoc or Bala beds being 

 repeated on the two sides of the anticlinal, but in great part con- 

 cealed on the south-east side by the overlapping May Hill or Upper 

 Llandovery rocks. These latter, as has been shown, form the true 

 base of the upper series which, in the Silurian sections, was repre- 

 sented by the Wenlock and Ludlow. Murchison had, by a strange 

 oversight, completely inverted the order of his lower series, and 

 turned the inferior members upside down. In fact, the Llandeilo- 

 flags, instead of being, as he had maintained, superior to the Cam- 

 brian (Caradoc or Bala) beds, were really inferior to them, and 

 were only made Silurian by a great mistake. The Caradoc, under 

 different names, was thus made to do duty at two horizons in the 

 Silurian system, both below and above the Llandeilo-flags. Nor 

 was this all, for by another error, as we have seen, the Caradoc in 

 the latter position was made to include the Pewtomerits-beds of the 

 unconformably overlying series. Thus it clearly appears that with 

 the exception of the relations of the Wenlock and Ludlow beds to 

 each other and to the overljdng Old Eed Sandstone, which were cor- 

 rectly determined, the Silurian system of Murchison was altogether 

 incorrect, and was moreover based upon a series of stratigraphical 



