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LLANDEILO FLAGS — BASE OF SILURIAN SYSTEM. 



tions are produced in them, similar to those to which I have alluded as occurring on 

 the sides of the trap rocks of Caer Caradoc. These transmutations will be described 

 in the next chapter. The Caradoc Sandstone is again exhibited in mountainous masses, 

 both in the south-western tracts of Shropshire, and largely in Montgomeryshire and 

 the adjacent parts of Denbighshire, particularly on the left bank of the river Ffyrnwy 

 near Meifod ; but the description of these masses is reserved, until I have explained 

 the linear outbursts of volcanic rocks, and the various anticlinal lines by which the 

 formations of the Silurian System have been broken up and separated. In the mean- 

 time we have sufficiently described the great and complex formation of the Caradoc 

 sandstone in the district where it emerges conformably from beneath the formations of 

 Ludlow and Wenlock ; and the descriptions of beds of similar age in other tracts will be 

 less diffuse. It may be remarked, that although so low in the series of deposits, the 

 formation is made up of beds of red, green, and purple sandstones, some of which it is 

 difficult, upon first inspection, to distinguish from strata of the Old, or even of the New 

 Red Sandstone. Its best and clearest distinctions consist, however, in its order of 

 infraposition to the upper Silurian rocks, and its organic remains, nearly all of which 

 are dissimilar from the fossils of the formations which immediately overlie it. 



Mines and Minerals. — Malachite, or the green carbonate of copper, occurs in thin 

 films and nests, and is occasionally slightly diffused through the sandstone of Longlane, 

 Soudley, &c. Copper ores were formerly worked in these beds near Cardington. These 

 veins lie near the contact of the deposits, with the trap rock of the Caradoc ridge, and 

 will be alluded to in the ensuing chapter. Thin strings of galena, with some associated 

 crystals of blende, have been also found in the south-western termination of this system 

 at Corston Heath, where the beds are also much dislocated and altered, but none of 

 these trials ended in profitable mining adventures. It will, however, be seen that in 

 other districts where trap rocks abound, beds of this age are penetrated by rich and 

 productive lead veins. 



" Llandeilo Flags," — 4th Formation. — Base of Silurian System. (I of woodcut, p. 196.) 



The Llandeilo flags are not seen in that district of Shropshire which has been 

 selected as affording the clearest and fullest types of the superior formations. They 

 have, therefore, been named after the town of Llandeilo in Caermarthenshire, where 

 they are largely developed. They consist of hard, dark-coloured flags, sometimes 

 slightly micaceous, frequently calcareous, with veins of white crystallized carbonate of 

 lime, and are specially distinguished by containing the large trilobites, Asaphus Buchii 

 (Brongn.), PI. 25. f. 2. ; and A tyrannus (Nob.), PI. 24. and PL 25. f. 1. Their relations 

 and peculiarities at Llandeilo will be described in the chapter on Caermarthenshire ; 

 it being sufficient now to state, that these flags there occupy various ridges, pass 

 under sandstones, the equivalents of those of the Caradoc, and are seen in some situa- 



