GRANITES AND ELVANS. 



231 



with white crystals of felspar, and nodules of clear quartz and black 

 mica embedded thickly. Schorl veins are there common. 



All these granites decompose so as to develop a tabular structure, 

 which is horizontal, and gives the rock a stratified appearance. 



In Kingston Down a hard granite alternates with a decomposed 

 granite so as to give a stratified appearance which coincides with the 

 dip of the adjoining slates. 



Alternations of schorl rock and granite give a similar stratified-, 

 appearance near St. Austell. 



At Pardenick Point, and other places near the Land's End, the 

 granite resembles a collection of huge basaltic columns. 



The Dartmoor granite is of post-carboniferous age, but it pierced 

 through a district which had previously experienced considerable 

 igneous action. Large veins, like dykes, are seen in the Serpentine 

 at Kynance, and in other places. The veins are generally a com- 

 pound of felspar and quartz. 



Elvans. The term Elvans is applied to long lines of granitic and 

 felspar porphyry rocks which cut the slates and granites, and there- 

 fore being newer are conveniently distinguished from the granite 

 veins which they occasionally resemble. 



The elvans have almost the same chemical and mineralogical com- 

 position as the granites, though their ingredients are differently aggre- 



1 J. A. Phillips, Q. J. G. S., vol. xxxi. p. 330. 

 3 Ibid., vol. xxx vi. p. 8. 



Ibid. 



