172 



IGNEOUS ROCKS OF WALES 



Upper 

 Galleky. 



Wall-case 4. 



Wall-case <&. 



Igneous Rocks of Wales and Shropshire 



Arranged by A. C. Ramsay. 

 Introductory remarks. 



Cas 



of Wales 



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% and 



The specimens in this case illustrate 



the Cambrian and Lower Silurian rt 



Shropshire. 



5 show the manner in which these rocks are associated with 



the strata. Each section has a title indicating the country 



it traverses. The rest of the writing indicates the names, 



places, and, in some degree, the nature of the different 



kinds of rock that form a great part of Wales, &c. A 



careful inspection of the sections, with a little knowledge 



and thought, will show the order of superposition of the 



different stratified masses that compose the country. 



The 



If 



loured grey. (Sections 1, % and a on the left, and s on 



the right.) 



The Loiver Silurian rocks succeed these, and consist at 



the base of Lingula beds, above which lie the Llandeilo 



flags, and these are succeeded by the Caradoc or Bala beds. 



All of them are coloured light purple except the Bala lime* 



stone marked by a thin streak of blue. These Loiver Silurian 



beds form the great mass of the country traversed by the 



sections, and in them, are all the contemporaneous Silurian 



[ Wales 

 Upper 



lie quite 



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the older strata. (Sections 



id 6.) The former in Shropshire and Wales are 

 always destitute of igneous rocks, and were deposited long 

 after the cessation of the volcanic eruptions that marked 

 the Lower Silurian epoch. 



The igneous rocks are of two kinds, eruptive and con- 

 temporaneous. By eruptive is meant those that have been 

 forced in a melted condition from below among the other rocks. 











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