544 Murch'usoris Silurian System. 



" The extent of the changes made in the map of the boundary lines 

 of previous observers, denning the junction of the old, and the contigu- 

 ous new red sandstone of Worcestershire, can be best understood by 

 comparison with such authorities. Much ambiguity, indeed, prevailed 

 in this part of the region, owing to the anomalous lithological charac- 

 ters of the lower new red sandstone, (already explained in chapter 4,) 

 which, on the confines of Worcestershire, Salop, and Herefordshire, 

 puts on so much the characters of the old red, with which it is in 

 contact. 



" On the right bank of the Tenu, the hills of old red sandstone, 

 ranging from Tenbury to the villages of Stamford and Shelsley Walsall 

 to Lapey, &c. consists of marls, clays, sandstones, and flags, with some 

 thick zones of concretionary limestones. In one of these bands r.ear 

 Hill Top, east of Tenbury, I found the crevices partially filled with 

 minute thin coats of anthracite, mixed with white crystallized car- 

 bonate of lime. Besides the principal bands of limestone, which here 

 vary in thickness from four to ten feet, there are, as in other places, 

 thinner courses of cornstone, alternating with beds of deep red and 

 greenish sandstones, of a flaggy structure. Much calcareous matter 

 is disseminated throughout these hills, and gives rise to the superficial 

 deposit of travertine and stalactite, which will be described in a sub- 

 sequent chapter. 



" The sandstones associated with the marls and cornstones sometimes 

 expose upon their surfaces certain small depressions, frequently of 

 circular and horse-shoe forms, occasionally having a raised central disc. 

 These forms, which are remarkably exhibited in the bed of the Sapey 

 Brook, near Knightsford bridge, appear to be due to the action of 

 water upon blotches, or imperfect concretions of party-coloured marls, 

 or soft argillaceous sandstones, which being of less consistence than 

 the mass of the rock, have been corroded, leaving these cavities. Similar 

 forms, indeed, are found in numberless portions of the old red sand- 

 stone. I may particularly cite the escarpment of the Skirrid, three 

 miles north of Abergavenny, and the cliff called the Dareu, north of 

 Crickhowell, as situations where they may be seen in countless profu- 

 sion, imitating in their outline, horse-shoes, rings, almonds, &c. It 

 is quite manifest that by exposing rocks of the varied composition of 

 these in question, to the action of running water, as in the Sapey 

 Brook, or to long continued atmospheric influences, as in the Skirrid, 

 the inevitable result would be the wearing away of these blotches or 

 concretions, which are softer than the inclosing mass of rock. 



" There is no district in which the nature and relations of the cornstone 



