Outlines of Geology. 239 



stone, and are seen forming the edges of the coal-basin. In some 

 places it is very bituminous, as on the Avon at Chepstow, and even 

 exudes petroleum. 



On the Welsh coast of the Bristol Channel we have another 

 ridge of limestone, forming the basin, as it were, in which the great 

 coal-field of S. Wales is situated. The hills that skirt Swansea 

 Bay, and much of the delightful scenery of Neath and its neigh- 

 bourhood ; the sudden slope which is crowned by Knoll Castle, 

 and the sinuosities of Pont-Neath- Vaughn, are characteristic 

 of this formation ; and again upon the banks of the Wye it con- 

 stitutes scenery of a soft, but most romantic character. Upon 

 the perpendicular and projecting precipices, lichensf of various 

 colours alternate with the gray surface of the uncovered rock. 

 A variety of shrubs are showered by Nature's hand upon its more 

 even, but still picturesque surface ; ivy, and other creeping plantSj 

 issue in gay luxuriance from its crevices, and its steep sides are 

 adorned by every variety of verdure. The charms of the valley 

 of Matlock, of Dovedale, and indeed of much of the Derbyshire 

 landscape, situated in the limestone glens, baffle all description ; 

 they have exercised the pencil of the painter and the pen of the 

 poet, but all their addresses to the eye and to the imagination are 

 cold and vapid , contrasted with nature's reality in these delight- 

 ful spots. 



I have formerly alluded to the occurrence of a red sandstone, 

 beneath the red marie accompanying the coal and salt deposits. 

 This is the old red sandstone of Wernerian geologists, and its 

 situation upon the lowest secondary rocks appears to give it a 

 title to that term. It often appears more as a conglomerate 

 than a sandstone ; that is, it is made up of coarse particles and 

 pebbles, and ranges of it are sometimes seen following those of 

 primitive rocks, where it is evidently composed of their d6bris. 

 Like many other rocks, it derives its colour from oxide of iron. 

 Geologists differ a good deal in their accounts of the position of 

 this rock in England. One place I may mention as affording un- 

 equivocal specimens of it, namely, the N. coast of Somersetshire 

 and Devonshire upon the Bristol channel, where it is seen recum* 



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