320 



TRAP DISLOCATING AND ALTERING LIMESTONE. 



Effects produced by the trap eruption of Old Radnor upon the contiguous limestone. 



The ordinary phenomena of sedimentary deposits, being altered and dislocated in contact with 

 trap, are displayed at numerous points around the hill of Old Radnor \ here the conglomerate is 

 raised into vertical walls between the trap and the limestone, there the shale is converted into an 

 indurated slate or Lydian stone. But besides these relations, the trap is seen in several places to 

 penetrate the limestone. This phenomenon is well shown at various places near the south-western 

 termination of the hill of Old Radnor, on both sides of the road leading to Gladestry, under the Ivy 

 Scar, at the Brook lime-kilns, &c. At the lime-works of Yat Hill, which are a few hundred paces 

 distant from the trap, the limestone dips at a slight angle from the hill and is regularly bedded, but 

 as it approaches the trap it becomes shattered, dislocated, and finally quite Mwstratified. Most of 

 the calcareous masses which have been quarried out at different levels from the abrupt face of the 

 trap are foetid, and the two or three feet nearest to that rock are usually in a highly brecciated and 

 altered state. A little west of the Ivy Scar, the limestone having been peeled off the face of the 

 trap rock, the thin coating abandoned by the workmen is in a brecciated state, resembling old 

 mortar, with an occasional seam of serpentine between the crystalline limestone and the trap. 



Here the trap forms a dyke about sixteen feet in width («), 

 having the frothy breccia (c) on one side, and bending over on the 

 other upon an irregularly bedded mass of limestone (Z>), the strata 

 of which dip very sharply to the north-east. In this case the trap 

 (compact felspar and decomposing greenstone) appears to have 

 risen through, broken up, and overflowed the limestone, twisting 

 back its elevated strata in the manner here represented. 



The serpentine which forms the back of the Brook lime quarries 

 is from twenty to thirty feet wide, the limestone in contact is very 

 hard, completely unstratified, and highly foetid under the hammer. 



55, 



a. Trap. b. Conglomerate. c. Unaltered limestone and shale. a*. Serpentine. c*. Altered limestone. 



In this locality the trap throws off to the west or opposite side of the quarry some beds of the 

 quartzose conglomerate (Z>), which by its dip passes under the regularly bedded adjacent lime- 

 stone (c). One of the pebbles from these beds appeared to have undergone fusion, and induced me 

 to think that some of this conglomerate might be of concretionary origin. On the other side of the 

 trap (a) the relations are very different, the intrusive rock being separated from the limestone by a 

 thin band of serpentine (a*), while the limestone itself (c*) is no longer stratified, but a hard, cry- 

 stalline, amorphous mass which has been deeply excavated. Where the serpentine folds over this 

 rock, its surface is polished. 



In every instance where similar phenomena have been laid bare around Old Radnor, the bands 

 of serpentine between the intrusive and the bedded rocks are more or less penetrated by veins of 

 calcareous spar, of which mineral there are no traces in the heart of the trap rock, which is then 

 either pure compact felspar, hypersthene, or greenstone. 



