No. 3.] HUNT — ON CAMBRIAN AND SILURIAN. 291 



An_irlesea repose directly upon the ancient crystalline schists. 

 According to the author of the Silurian System^ there existed 

 beneath the base of the Llandeilo formation a great con- 

 formable series of slaty rocks into which this formation passed, 

 and from which it could not be distinguished either zoologically, 

 stratigraphically or lithologically. The sequence, determined 

 from what were considered typical sections in the valley of the 

 Towey in Caermarthenshire, as given by Murchison, for several 

 years both before and after the publication of his work, was as 

 follows : 1 . Cambrian ; 2. Llandeilo fligs ; 3. Caradoc sandstone ; 

 4. Wcnlock and Ludlow beds; 5. Old Red sandstone; the order 

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

 siliferous Cambrian beds underlying the Llandeilo and indistin- 

 guishable 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 undulaticns 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 unconform- 

 able upper series which includes the Wenlcck and Ludlow beds. 

 [Philos. ^lag. IV, vili, 488.] The section to the s'^uth-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, partially 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. Ramsay, 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 iu fact: 1, 



