XV.] CAMBRIAN AND SILURIAN IN EUROPE. 361 



results of the government surveyors'? The Llandeilo rocks, 

 having throughout the characteristic Orthis so much insisted 

 upon by Murchison, were shown to be the base of a great 

 conformable series, and to the' eastward, in Shropshire, to rest 

 on the upturned edges of the Longmynd rocks ; while west- 

 ward, near Bala, they overlie unconformably the Lingula flags, 

 and in the island of Anglesea repose directly upon the ancient 

 crystalline schists. According to the author of the Silurian 

 System, there existed beneath the base of the Llandeilo forma- 

 tion a great conformable 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 sec- 

 tions in the valley of the Towey in Caermarthenshire, as given 

 by Murchison, for several years both before and after the pub- 

 lication of his work, was as follows : 1. Cambrian ; 2. Llan- 

 deilo flags ; 3. Caradoc sandstone ; 4. Wenlock and Ludlow 

 beds ; 5. Old Eed sandstone ; the order being from northwest 

 to southeast. What, then, were these fossiliferous Cambrian 

 beds underlying the Llandeilo and indistinguishable from it ? 

 Sedgwick, with the aid of the government surveyors, has an- 

 swered 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 anti- 

 clinal in the valley, and are succeeded to the southeast by a 

 portion of the Bala. The great mass of this group on the 

 southeast side of the anticlinal is however concealed by the 

 overlapping May Hill sandstone, the base of the unconform- 

 able upper series which includes the Wenlock and Ludlow 

 beds. (Philos. Mag. (4), VIII. 488.) The section to the 

 southeast, commencing from the Llandeilo flags on the anti- 

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

 great mass of strata on the northwest side of the Llandeilo 

 (which is the complete representative of the Caradoc or Bala 

 beds, partially concealed on the southwest side) was supposed 

 by him to lie beneath the Llandeilo, and was called Cambrian 

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