542 MurchisorTs Silurian System. 



laid open by making the new road from Chepstow to Usk, which runs 

 directly across the strata. On this road the traveller first passes over 

 the quartzose formation of sandstone and conglomerate, rising from 

 beneath the lower carboniferous limestone shale, next the marls and 

 cornstone in the bold escarpment of Golden Hill, and thence traversing 

 sundry calcareous courses, he meets with the Silurian rocks in the hills 

 north of Usk, throwing off upon their eastern slopes the marls and 

 tilestones. In the southern parts of Herefordshire (between Mon- 

 mouth Cap and Whitefield), are numerous courses of small round con- 

 cretions, which not being firmly bound together by the matrix, readily 

 separate from the imbedding sand and clay, and are used as gravel for 

 the roads. In the same tract, however, are strong courses of very 

 pure concretionary limestone, of purple and green colours, one variety 

 of which appears to have been formerly used as marble. 



" To the north of the river Wye, the same system is prolonged in the 

 central hills of Herefordshire ; and traverses made across these hills 

 from Hereford to the Vale of Woably, afford good sections of the corn- 

 stone group. The descending section of it may be thus enumerated, 

 the beds dipping to the SE. or SSE. at angles of 12° and 15°. 



" a. Slaty beds quarried for tiles in the hills above Mr. Peploe's Park 

 (contain broken portions of vegetables often in a state of carbon). 

 " b. Marls, red and green. 



" c. Cornstone, in parts semi-crystalline, seldom exceeding 4 to 5 feet 

 in thickness. 



" d. Argillaceous marls with impure limestone, fit only for road-mend- 

 ing. 



" e. Great sandstone quarries (at Rauen's causeway, for example), 

 from 30 to 40 feet in depth contain fine large flaggy beds of light 

 greenish colour, used for tombstones ; and strong beds of micaceous, 

 finely grained sandstone ; the lines of deposit being sometimes marked 

 by purple and light green stripes. This stone is of excellent quality for 

 building. 



"/. Argillaceous marls. 



" g. Courses of impure concretionary limestone appear here and 

 there in the slopes and lower sides of the hills ; these descend into the 

 rich low ground around Weobly. If powerful denudation had not 

 destroyed the strata and covered them with gravel, the valley of the 

 Wye, between Hereford and the Hay, would doubtlessly have afforded 

 similar sections, for the same succession of argillaceous marl, sand- 

 stone, cornstone, and flagstone is displayed in the hills of Moccas 

 on the south or right bank of the Wye, as those described in the 



