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GRANITIC PORPHYRIES. 



237 



this locality, ( 



and composed of a quartz 



and felspar base, in which plates of black mica and crystals 



/< 



This is one of the many granite veins (see Map 



which cut through the slates 



Blisland. 



30,) 

 in the neighbourhood of 

 Is employed for the roads, for which it is a <?ood 

 material— London Inn, near Cardinham, Cornwall. 



1 02.— Felspar porphyry.— Flesh-coloured felspathic 



base. — 



containing crystals of white felspar and 



ana quartz. 

 °0. 



(See No. 104.) Part of an el van dyke. Map „. 



Would form a very beautiful material for ornamental 

 purposes ; there are also some grey varieties that would bo 

 by no means inferior.— Tremore, near Bodmin, Corn- 



wall. 



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103. — Granitic rock, composed of 



r 



No. 83. 



and hornblende, 

 *fi 



J. 



containing 



Treburget, near St. Teath, Cornwall. 

 104. — Felspar porphyry. 



a grey base of 



imperfect crystals of 



Map 30. A variety of 



f/< 



Flesh-coloured felspathic 



"> 



f 



quartz, and with a greenish substance not very determin- 



Fornis part of a long line, apparently intruded anion* 



able. 



( 



tending from Tremore near Bodmin to Tregotha near 



•St. Wenn. 



In the lane leading from St. Wenn Church to Lancorlar, 

 and also in the road to Eestigen, this dyke is seen to be 

 irregularly decomposed so as to appear like a white or pink 

 clay containing quartz crystals, and crystals of felspar, the 

 latter being decomposed. This decomposition does not ex- 

 tend beyond the distance of live-eighths of a mile, 

 polished it would form a valuable ornamental stone.. 

 Wenn, Cornwall. 



If 



St. 



105.. 



dt 



Granitic porphyry, composed of crystal 



S 



■f/7, 



few spots of 



schorl m a light-grey felspatho-quartzose base, and contain- 

 mg cracks filled with translucent quartz and schorl. 



Wall-cas 

 6 and 7. 



es 



