WENLOCK AND CARADOC FORMATIONS NEAR USK. 



Llaiigibby Hills, particularly in the steep descent from the "high beech" to Prescoed, where the 

 perishable mudstone is many hundred feet thick. The rocks of this formation occupy, on the 

 whole, the highest hills of this Silurian tract, and, like those of Woolhope Valley, are excavated 

 deeply at their escarpment, leaving a valley between them and the Wenlock Limestone, the next 

 hard rock in descending order. 



" Wenlock Limestone.' 3 



This limestone constitutes a low narrow zone, which circling in pretty regular curves for two or 

 three miles in the southern portion of the tract folds over the Caradoc Sandstone of Prescoed Com- 

 mon, and dips at low angles to the east, south-east and south, beneath the Ludlow Rocks. After 

 an interval in which the limestone is not distinctly traceable, it reappears in a very prominent ledge 

 of about two miles in length, forming the eastern side of Glasgoed Common, along which it has 

 been extensively quarried, the beds dipping to the west at angles of 8° and 10°, and passing under 

 the Lower Ludlow Rock. 



The limestone has the same characters as in Shropshire and Herefordshire. We perceive the 

 same small concretionary nodules of impure limestone, here called "bowls" by the workmen, 

 passing down into hardish, dull, earthy limestone, or calcareous grit, which sometimes alternates 

 with courses of whitish yellow clay, and is underlaid by a subcrystalline encrinite limestone, thinly 

 bedded in the upper but thickly in the lower part. In some places the strata composing the 

 latter have a considerable thickness, and are occasionally mottled pink and greenish grey, in which 

 cases they are un distinguishable from certain beds near (Easthope) Wenlock Edge. A fine section 

 of the thick bedded grey limestone is exposed in the quarries of Cil-na-caya, the strata dipping 25° 

 beneath the hills of Ludlow Rock, and containing many good fossils. 



The lower shale is here clearly seen beneath the limestone, and weathers to the same light ashen 

 colour as in Salop. The analogy with the Shropshire beds is completed, by finding many large con- 

 cretions or "ball stones" ten and twelve feet thick, which swell out suddenly and throw off the 

 strata either abruptly or in undulations, as shown in the figures (pp. 210 and 211), for which reason 

 the workmen here term them the " old horses," meaning thereby, that the regular beds ride athwart 

 them. In these " ball stones " the limestone is as crystalline as in Wenlock Edge, and contains many 

 specimens of "chain" coral and other characteristic fossils. 



" Caradoc Sandstone." 



The Caradoc sandstone constitutes the nucleus of this tract, and occupying the dome-shaped 

 mass of Prescoed Common, and the Hills of Cilfigan Park and Bryn Craig, dips on all sides 

 beneath the Wenlock Limestone. Tentaculites and circular ferruginous casts of crinoidal stems, 

 mark the surfaces of these thin bedded sandstones, in the same manner as on the eastern slopes 

 of the Caradoc Hills. The escarpment of Bryn Craig explains clearly the relations of these beds : 

 they there dip under the Wenlock Limestone of Glasgoed, a very thin mass of shale being inter- 

 posed ; whilst in the descent to the Tucking Mill, they are underlaid by a considerable thick- 

 ness of shale, which weathers to a light colour and forms a cold soil. This shale is a local 

 peculiarity in the mineral structure of the formation. It is, however, to be observed, that as 

 they are here but slightly developed, they may represent those beds described at the base of the 



