61 



applies to veins called dykes, horublendic seams interstratilied 

 in sedimentary beds ; such as the Whin sill of the North of En- 

 gland^ veins of carbonate of lime, &c, that is, they are forced 

 into the joints in an aqueous state subsequently to the formation 

 of the inclosing beds. 



A very interesting article on this subject appeared in the 

 Mining Journal, which appears to have been written by a prac- 

 tical person who had examined such a formation near Wolver- 

 hampton : the following is an extract: — 



" Some geologists not only maintain that the trap rocks which 

 are interstratified amongst the beds of the carboniferous rocks of 

 England were forced into their present positions in an igneous 

 state, but they also point out the centres of eruption from which 

 they were injected into the coal measures. Several such centres 

 of eruption had been long pointed out in the Wolverhampton 

 district ; but, like numbers of other questionable points on this 

 subject, persons seldom take the trouble of contradicting them, 

 by giving a bond fide representation of the facts, to check the 

 progress of such igneous absurdities. 



" The occurrence of the large masses of green rock, called 

 'trap,' at Pouk Hill, the Nechells, and other localities in the 

 Wolverhampton district, is not owing to these points being cen- 

 tres of eruption, but simply to the bed of greenstone (which is 

 hornblendic) throwing off branches from its upper surface, which 

 branches in parts are exposed on the surface ; the under part 

 of the above bed of trap maintaining its position unchanged, and 

 the coal measures ranging underneath it, in a comparatively un- 

 disturbed state, as observed in the workings below, showing very 

 clear that the disturbance in the district is confined to the upper 

 part of the series, and proceeding solely from the action of the bed 

 alone upwards, and not from an igneous intrusion from below. 



" This trap, or hornblendic bed, is always moist, and in parts 

 as soft as clay ; and when this happens to be the case, the dis- 

 turbance appears to be greatest, and the beds in contact are often 

 seen fractured, and saturated with mineral water, and the cracks 

 filled with calcareous and siliceous spar proceeding from the large 

 bed of trap, — and, as the upper beds present the least resistance 

 to the swelling or apparent increasing power of this rock, the 

 fractures and veins are formed upwards, and bear the same 



