272 ALTERNATIONS OF VOLCANIC GRIT AND LOWER SILURIAN ROCKS. 



Transverse sections at the southern end of this district, i. e. from the Linley Hills to Taudley, pass- 

 ing near Hyssington, expose similar repetitions of bedded trap, sometimes forming distinct ledges, 

 which alternate with shale and sandstone, altered and unaltered. In these ridges and furrows the 

 dip of one range of high ground being to the west, that of the next is usually to the east, and gene- 

 rally at angles of 40°; so that by anticlinal and synclinal lines there is a folding over and repetition 

 of the same strata as in the Lordstone and Callows Hills, dependent doubtless upon parallel lines 

 of eruption. (PL 32. f. 3.) These ridges are prolonged to the north-north-west into low hills upon 

 the sides of the road near Grimmer, between Minsterly and Leigh Hall, where they subside, 

 together with certain bosses of amorphous trap which appear upon their flanks. At Hyssington 

 Common, near the other extremity of the chain, the lowest visible masses dip to the east, and 

 consist of thick and thin beds of light- coloured, felspathic conglomerate, occasionally containing 

 crystals of common felspar, but here and there becoming coarse with entangled fragments of schist. 

 These are overlaid, on the dip, by hard, dark grey or blue, felspathic amygdaloid, in parts assuming 

 a columnar structure. Though bedded on a large scale, this rock seems to have somewhat an irregular 

 direction, and to throw off the strata in a highly altered condition, including thin courses of white 

 china stone, nearly resembling the porcellanite of Whitsborn Hill. (See p. 275.) In following 

 these courses of altered rock, trap, and shale, to the old castle of Hyssington, the dip increases 

 from 45° to 70° and 80° j but amid much contortion the strike is preserved to the north-north-east. 

 Between Hyssington and Hurdley, (on the flank of Taudley) the dip of the strata is again com- 

 pletely reversed, and they are inclined to the west-north-west 1 . In Sunny Bank is an outburst of 

 trap rock wholly unbedded, which is prolonged in low knolls to the east of Hurdley, throwing off 

 the strata sharply to the west. This felspar rock, both granular and compact, has a conchoidal 

 fracture and rude columnar form, and is fissured by many rents and cracks ; it is in parts amygdaloidal, 

 with nests of green earth and crystals of felspar, and has been extensively quarried as a coarse 

 building stone. On the west this intrusive rock is again flanked by schists, whicl are overlaid by 

 thick and thin beds of the hard felspathic agglomerate, with fragments of schist, containing many 

 crystals of iron pyrites. These massive trap beds, which are also much quarried as road stones, dip 

 60° west, and are overlaid by slaty porphyry and grey granular felspar rocks, and highly indurated 

 schists, alternating in courses a few inches thick each. In Brith-dir to the north of Hurdley, and 

 on the flank of Roundtain, similar examples of alternation of trap and shale (the prolongation of the 

 same beds) are exhibited on a large scale. The trap is for the most part a mottled felspar rock, 

 with crystals of common felspar and nests of decomposed iron pyrites. It is worthy of remark, 

 that the strike of these linear masses from Brith-dir to Hurdley, or those on the eastern side of 

 Roundtain and Taudley, is very nearly north and south ; and those upon the western flank of those 

 hills due north and south, being a difference of 25° from the direction of all the other pro- 

 minent ridges of the district. This diversity or apparent folding round near the end of the chain, 

 seems to indicate, that the sediments have been thus arranged round the great centre of eruption of 

 this volcanized tract, dipping away from it on all sides. 



A great many examples have been cited of the intimate manner in which the strati- 

 fied trap of this district alternates with the ordinary sedimentary deposits, to convince 

 the reader that such dejections must have taken place during the formation of those 

 Lower Silurian rocks with which the volcanic matter is interstratified. I would only 

 further add that these bedded trap rocks so completely assume the features predominant 



1 The black shale at Llanerst contains trilobites. 



