102 



QUARTZ ROCKS AND 



Upper 

 Gallery. 



spongy 



This is still more obvious below. The slates W 



Wall^se45. t^* T^I ^^ T*** °* ^^ *» 0r &»*> "* 



being softened by heat they have been bent. Similar rocks 

 altered by contact with igneous rocks under great pressure 

 do not assume this vesicular structure. For instances of strata 

 altered by contact with melted rocks, see Nos. 9, 12 &c. 

 5 — Gornal sandstone, unaltered. Coal Measures. ' 

 6. — Gornal sandstone, altered, artificially. 

 This specimen formed part of the hearth of an old iron 

 furnace. From long contact with the melted iron the 

 stone ^ was softened and partly vitrified, and cinders are 



Tlie vitrification was assisted by the 

 presence of numerous felspathic grains which are minted 



embedded in it. 



with the quartz grains of the Gornal sandstone. 



7— Q 



Hi 



Old IZad- 



7. The quartz rock in its unaltered state was pro- 

 bably the equivalent of the fossilliferous sandstone of Pres- 



teign : 



May Hill 



8.— Altered sandstone, crystalline and calcareous. 



Radnor H 



This hill occurs on a line of great disturbance and frac- 

 ture, into which syenitic and greenstone rocks have been 

 protruded. On Old Radnor Hill the rock is so highly 

 altered and so intimately intermixed with igneous matter 

 that it is impossible to separate the altered rock from that 

 which produced the alteration. This specimen gives a good 

 example of the intense alteration of the sandstone, and inti- 

 mate intermixture of igneous matter with it. 



9. 

 Golfc 



Q 



fags 



Moel 



10.— Greenstone of Breidden Hills, with which the al- 



No 



11. 



Granular quartz rock, commonly called Lickey 

 quartz, with grains of felspar.— From Caradoc sandstone 

 of Rubury Hill, Worcestershire. 



There is no igneous rock intruded into this mass, which, 

 notwithstanding, has an altered character, and it is not 



7 





II, On 

 if slate, 



18— i 



.It 



m o 



it 



if I 



(» 



U 



i\ 



20, 



k 



"Oft] 



una 



