276 AN ENQUIRY INTO THE NATURE OF [Ch. XIII. 



these veins contains a second vein, holding a serpentine 

 course through the first in a somewhat parallel direction, and 

 readily distinguished by being formed of a much more black, 

 durable, and compact basalt. These veins are often stratified, 

 or, more properly speaking, laminated in the direction of their 

 length. Their direction is almost invariably either vertical 

 or slightly inclined from the plumb ; and they present, there- 

 fore, a perpetual parallelism along the coast. They are 

 equal throughout, and never ramify ; and although they vary 

 from five feet to twenty in breadth, they seldom exceed ten 

 feet. Although these veins are so large and numerous, not 

 the slightest disturbance takes place in the evenness and the 

 horizontally of the strata of sandstone which they intersect : 

 there is neither contortion, bending, fracture, nor displace- 

 ment ; nor do they appear to have affected the texture of the 

 rock, since it is the same both at the place of contact, and at 

 a distance therefrom. Nor must it be omitted to remark, 

 that these trap-veins, in some places, nearly equal in extent 

 the stratified rock through which they pass. If the lateral 

 dimensions of these veins collectively be assumed to equal 

 one-tenth part of the stratified rock (and this estimate does 

 not appear to be excessive), the latter rock must have under- 

 gone a lateral extension equal to that quantity ; a motion so 

 great, that it is extremely difficult to reconcile it with the 

 present apparent repose and regularity of the whole.* 



The occurrence of trap-rocks, among the carboniferous 

 and older greywacke groups, has been recorded by many 

 observers : sometimes they intersect these strata without pro- 

 ducing any alteration in their position, but very commonly 

 they produce displacements, the strata, on one side, being at 

 a different level to those on the other ; and when many trap- 

 dykes occur, then there is a great complication of these 

 appearances, as also when only seams of dislocation are pre- 

 sent, as in the case of the Jarrow Colliery, near Newcastle. 



* Gcol. Trans., vol. iii, p. 79. et seq. 



