Murchisori s Silurian System. 551 



ing beds. Mr. Murchison remarks that the dyke lies in 

 the direction of the elevated mass of Shuckness Hill, distant 

 three miles from the spot at which the dyke is opened, and 

 infers accordingly that the hill is connected with a line of 

 disturbance occasioned by this dyke. 



The second dyke is exposed by quarries near the Teme, 

 eleven miles north-east of Worcester, and distant about a 

 mile from the Abberley Hills, which follow its course. The 

 dyke is at one place where it is exposed to a depth of 40 

 feet, about eight paces wide, and near its walls the trap 

 assumes a prismatic form, decomposing like the basaltic 

 columns of the Giant's Causeway. The composition of this 

 dyke is unique, being partly dark green syenite, and partly an 

 amygdaloid, containing kernels of carbonate of lime, which 

 on exposure fall out, leaving cavities in the sides of the 

 prisms. On either side of the dyke the sandstone is 

 hardened and of dark purple colour, and the variegated 

 marls and cornstone are converted into an indurated mass, 

 resembling many trappean amygdaloids, and the lime is dis- 

 seminated in veins and coatings of white crystallized car- 

 bonate of lime. This dyke is analogous in its structure, Mr. 

 Murchison states, to some parts of the Malvern ridge, and as 

 it points to the most prominent of those elevations, we obtain 

 one of the proofs that volcanic forces have been in activity 

 along the great fissure of eruption subsequent to the conso- 

 lidation of the old red sandstone. " Again, from the highly 

 dislocated condition of the patches of coal which adhere to 

 the flanks of these hills, no doubt can remain that volcanic 

 action was also continued upon this line after the deposit of 

 the carboniferous system". With the evidence we shall after- 

 wards adduce, says Mr. Murchison, of the frequency of 

 trappean eruptions during the formation of the Silurian sys- 

 tem, and with the proofs we have already given of the out- 

 burst of such rocks subsequent to the consolidation of the 

 coal measures, it is surprising that during the accumulation 



