198 THE GEOLOGICAL AGE OF CENTRAL AND "S^EST CORN"^ALL. 



in the most complex manner. Mr. Barnett lias described these 

 veins with much accuracy in his paper already referred to. The 

 accompanying figure, shewing the chief branches of the vein 

 (No. 34) somewhat nearer the headland, is copied from that 

 given by him. 



Fig 7. — Newqjtay Neck. 



No. 35. "Watergate Bay. This dyke is marked on the survey 

 map as an elvan running very nearly N.S. and extending for 

 eight or nine miles. In several places where we have seen it, 

 its appearance is much more that of a trap than an ordinary 

 elvan — i.e. it is a basic rock — containing much mica. It often, 

 too, exhibits a strong tendency to spheroidal structure, but we 

 regret that we have no specimens by us which we could analyse. 



We have thus in an area of not more than 25 miles by 10, 

 35 or more distinct outcrops of a rock which, until lately, was 

 supposed to be limited in Britain to the Cumbrian district.'^' 



The essential unity of character of composition in this system 

 of veins — hitherto spoken of variously as "trap," "elvan," 

 "sandstone," or "marl," has only been ascertained by careful 



* "Mica traps so fax* as we are aware, are either very rare or wholly absent in 

 Britain to the south of the Cumbrian district, and in that they are rarely found 

 in the vicinity of the principal lakes, but are almost confined to the eastern part 

 of Westmoreland and the north-western of Yorkshire, ahvays occurring in 

 Silurian rocks." Bonney and Houghton, Quart. Journ. Geol. Soc. 1878, 137, p. 

 165, It is worthy of remark that most (but not all) of the Cornish veins occur 

 traversing Silurian rocks, as do also those of Bohemia. 



