ALTERED ROCKS. — NASH SCAR. 



321 



Nests and thin coatings of anthracite are also of frequent occurrence on the exterior of the trap, 

 and are occasionally found some distance within the altered bedded rocks, associated with minute 

 veins of copper ore and crystals of copper and iron pyrites. 



At other points of contact where the trap throws off the shale, the latter is in a highly indurated 

 state, almost Lydian stone, and breaks into numerous small fragments 1 . 



The phenomena of the altered deposits in contact with the trappean hills of Old 

 Radnor are in many respects analogous to those observed in other parts of this region, 

 with the difference, that the actual insertion of the trap into the limestone, and the 

 consequent alteration of the latter, are more plainly exhibited than in Shropshire. 

 Comparing small things with great, I may say, that the changes at Old Radnor are 

 precisely analogous to those of the Val di Fassa in the Tyrol, where numerous dykes 

 and protruding masses of trap, carry up on their flanks dislocated portions of shale and 

 limestone, the latter being frequently changed into a marble, usually separated from the 

 intrusive rock by a similar coating of serpentine. In the alterations of the Silurian 

 formations, we have every proof that the intrusive volcanic rocks penetrated the lime- 

 stone posterior to its consolidation. Not only are the traces of bedding obliterated 

 as the strata approach the trap, but the whole texture of the rock is changed ; being 

 converted from an ordinary, earthy, sub-crystalline limestone into a mottled, veined, 

 and hard marble. Shells and way-boards of division, so common in the strata a few 

 paces from the trap, disappear in these amorphous masses of limestone, which exhibit, 

 on the contrary, veins and nests of anthracite, copper ore, &c. 



The effects of the subterranean agents which produced these changes at Old Radnor are not con- 

 fined merely to the flanks of that hill. We find that the line of this axis of elevation has been 

 prolonged to the north-east through the Nash Scar to Gorton turnpike-gate, in which space the 

 same causes must doubtless have operated ; for although no trap is visible, the magnificent mass 

 of highly crystalline and altered limestone, a part of which is represented in this wood-cut, 



56. 



1 The Right Honourable Frankland Lewis and his son Mr. George Lewis accompanied me in an examination 

 of these rocks, and were of essential use in directing my attention to points of interest. 



