CHAPTER XXIV. 



Range and Distribution of the Silurian Rocks in Montgomeryshire and the adjacent 

 Districts of Shropshire and Denbighshire. (PI. 32. figs. 1, 2, and 9. PL 33. 



f.i.) 



In the three preceding chapters it has been shown, that the Longmynd and adjacent 

 hills constitute a mineral axis, in which certain rocks of the Cambrian System throw off 

 the Silurian deposits on their flanks ; that the Silurian rocks to the west of this axis 

 have been the theatre of intense volcanic action and are the seat of valuable mines ; 

 and that the Breidden Hills, still further to the west, have been formed by another out- 

 burst of volcanic matter. Having attempted to fix the eeras of these eruptions, and to 

 explain the effects they have produced upon the sedimentary deposits, I now proceed 

 to the consideration of the strata composing the Silurian System which are spread over 

 the south-western parts of Salop and wide tracts of Montgomeryshire and Denbighshire. 

 We shall thus complete the account of these deposits over one large district before we 

 follow them into South Wales. 



The Silurian strata which occupy this large tract, lie in several undulations or troughs, 

 between the districts already described and the Berwyn Mountains, constituting in fact 

 a number of parallel anticlinal and synclinal lines. (See transverse section, PI. 32. f. 9.) 

 The Ludlow Rocks, properly so called, extend over a large portion of the eastern side 

 of this area. In the environs of Clun and Bishop's Castle, they occupy the hills of 

 Clunbury, the Black Mountain, &c, and sweeping round by Stow Hill to Knighton, 

 they support the great detached outlier of Old Red Sandstone of Clun Forest, forming 

 Kerry Hill on the west, and on the north and north-east the hills of Bishop's Castle, 

 Walcot Park, Eyton and Bury Ditches. (PI. 33. f. 1.) Wherever the Silurian rocks 

 are near the Old Red Sandstone, as at Clun, they consist of the true Upper Ludlow 

 Rock, characterized by Homalonotus Knightii, Serpuloides longissima, Lept&na lata, 

 Orbicula rugata, Cypricardia amygdalina, Orthoceratites, and other well-known fossils, 

 and have precisely the same mineral characters as the rock in the immediate vicinity 

 of Ludlow, being also quarried for the same purposes. In this range they vary in 

 height from 800 to 1400 feet, the strata upon the whole dipping inwards, and forming 



