130 



DISLOCATIONS CAUSED BY BASALTIC ERUPTIONS. 



these hills the basalt is either in a broken state, or has been penetrated in search of 

 coal ; but at the northern part of this Barf, trials made eighty or ninety years ago to a 

 very considerable depth, still left off in a mass of solid basalt. "We may therefore pre- 

 sume that this was a funnel of eruption, and that from this point the igneous matter 

 flowed over, and covered the coal measures of the adjacent Clee Barf ; for there, as be- 

 fore stated, the basalt is a mere sheet which has repeatedly been penetrated in search 

 of coal. If such were the case, vast changes, however, must have taken place since the 

 emission of the basalt ; for there is no longer any continuity between the mass on the 

 summit of the Clee Barf, and the point of eruption at Abdon Barf, the higher and the 

 lower summit being separated by a depression occupied by the Old Red Sandstone. 

 The relative altitude, however, of the two hills tends to favour the belief, that the 

 basalt capping the lower hill, originally descended from the higher point of eruption, 

 the intervening or connecting mass having been since denuded. 



It has already been shown, that the Brown Clee Hills have been affected by two sets 

 of faults, the one from north to south, coincident with the main direction of the ele- 

 vated mass or major ellipse of the coal tract, the other from east to west, or transverse 

 to the chief direction of the ridge. 



Some of these fractures were doubtless produced after the period of great volcanic 

 activity, though it has been clearly proved, pp. 127, 128, that the most powerful dis- 

 locations were directly the result of basaltic eruption. Again, the discovery of the sub- 

 terranean cone of trap rock described, p. 129, leads us naturally to suppose, that such 

 agents may have caused some of the contiguous faults j for similar hidden and conical 

 masses of igneous rock may exist at other points. 



There is, indeed, no difficulty in reading off the method by which this tract has at- 

 tained its present relations ; for here we see a coal-field placed at a higher level above 

 the sea than any other in Great Britain, affording on its sides and in its centre the 

 clearest proofs of having been heaved up into its present position by powerful forces 

 acting from beneath, which have thrown the carbonaceous masses into separate troughs 

 or basins j whilst the ground is rife with volcanic rocks to testify, that the heat which 

 evolved them, and the earthquakes which accompanied them, must have been the agents 

 in dismembering those carbonaceous strata which were once spread out continuously 

 beneath the sea. 



Without anticipating subsequent observations I would remark, in passing, that here 

 as at Coal Brook Dale, the best-defined line of outburst, or that of the Hoar Edge and 

 Cornbrook fields, is parallel to other and more ancient lines of eruption in the Caradoc 

 Hills, of which we shall treat in the sequel, as having elevated the Silurian rocks. 



