318 



OLD RADNOR TRAP. — STANNER ROCKS. 



group ; the central or chief mass is included between Llandrindod and Llandegley on the 

 north-east, and Builth on the south-west, whilst a third and very short ridge, precisely 

 parallel to the others, occurs at Baxter's Bank, five miles north-west of Llandrindod. 



" Old Radnor Group." 



The trap of these hills bursts out through the formations of the " Silurian System," 

 throwing off the Ludlow Rocks of Bradnor Hill and Hergest Ridge to the south-east, 

 and breaking up the inferior shales and the Wenlock limestone in the vicinity of Old 

 Radnor. It occupies two distinct parallel ridges, separated by a valley of shale and 

 limestone. The eastern, about three miles in length, comprises the Stanner Rocks, 

 Worsel Wood, and Hanter Hill, which are severally 1000, 900, and 1200 feet above 

 the sea ; the western, called Old Radnor Bill, is 1100 feet in height, and only half the 

 length of the other 1 . The vale inclosed between these ridges communicates with the 

 low country, upon the east, by a transverse depression, which separates Stanner Rocks 

 from Worsel Wood and the hill of Bradnor from that of Hergest, both composed of the 

 Ludlow formation. (See PI. 33. f. 3.) 



Stanner Rocks. 



The north-eastern extremity of the trap of this hill ranges into low hummocks between the farm 

 of Old Harpton and the south-western flank of Herrock Hill, whence it is traceable into the narrow 

 ridge of Stanner Rocks, forming the foreground of the sketch prefixed to this chapter, which, rising 

 to the height of 1000 feet, terminate opposite Worsel Wood in a precipitous cliff*. The trap of this 

 and the adjoining hills resemble the hypersthene rock of Coruisk in the Isle of Skye, described by 

 Dr. MacCulloch 2 . Like the rocks of Coruisk (which I have examined in situ) these of Old Rad- 

 nor pass from a coarse crystalline hypersthene rock into fine-grained greenstone, in which the 

 separate crystals of hypersthene are no longer perceptible. The base, however, is for the most part 

 dissimilar from that of Skye in the white and sometimes pink colour of the felspar, and in containing 

 also mottled and slaty varieties of compact felspar, some of which are of a bluish colour, glossy 

 surface, and brittle fracture. The felspar rocks are also granular, and in some few instances por- 

 phyritic. In the vertical cliff, in addition to numerous varieties of hypersthene, felspar rock and 

 greenstone, is a very hard compact stone of a black colour and polished surface, probably an intimate 



1 The sketch facing the first page of this chapter represents the eastern ridge ; Stanner Rocks in the fore- 

 ground, with Worsel Wood and Hanter Hill beyond. The high ground in the distance is Hergest Ridge, 

 composed of the Ludlow formation. 



2 On referring a fragment of this rock to Professor Miller of Cambridge he has favoured me with the follow- 

 ing account of it : — "The dark mineral has one very perfect cleavage, and a dull face or imperfect cleavage 

 nearly at right angles to the former. Alone, on platina wire, it is fusible with difficulty. It dissolves slowly 

 but completely in borax, giving a head coloured by iron. The powder of the mineral is not sensibly acted upon 

 by hot sulphuric acid. It scratches fluor. The mineral is probably the variety of augite (hornblende), called 

 diallage, brongite, or hypersthene." 



