Geological Society, 227 



here and there, and at Lyds Hole are jaspidified red sandstones, 

 with abundant veins of carbonate oflime, &c., the whole being in a 

 state of extreme contortion and irregularity. 



Shelve, Corndon, Sfc— The mining district of Shelve is an iso- 

 lated tract, separated from the Linley and Longmynd Hills by the 

 remarkable ridge of quartz rock, called the Stiper stones. It is 

 made up of parallel ridges of trap, and alternating depressions in 

 grauwacke. The trap rocks of this district are greenstones, por- 

 phyries, claystones, &c. These are separated by the author into 

 two classes ; the one, alternating conformably with the strata of the 

 third and fourth grauwacke formations, is supposed to be contem- 

 poraneous with them j the other is shown to be posterior to the 

 consolidation of the stratified deposits. In the contemporaneously 

 formed traps are several varieties, some of which, although aggre- 

 gates of compact felspar with a concretionary structure, contain 

 organic remains : others graduate into the class of volcanic sand- 

 stone. The first are best seen near Leigh Hall, the latter in the 

 Corndon flagstones, Mary Knoll dingle, &c, where they are largely 

 quarried. 



The other class, or the intrusive trap, rises to the greatest heights 

 and to the largest masses in the Corndon, Stapely, Taudley, and 

 Roundton Hills, which form the chief axis of the district ; but there 

 are other linear eruptions, many of which are of extreme tenuity, 

 occasioning numerdus alternations of trap and grauwacke. The 

 trap rocks consist of greenstones, porphyritic greenstone, compact 

 felspar, concretionary felspar simple and porphyritic, amygda- 

 loids, &c. 



Some remarkable parallel dykes are described running from north- 

 east to south-west between beds of grauwacke, shale, and calcareous 

 flag, which latter in some instances is converted near the prismatic 

 ends of these dykes, into cream-coloured porcellanite. In the 

 grauwacke adjacent to the trap are also many productive veins of 

 lead, which are respectively described at the Snailbach, Penally, 

 Bog, Gravel, Grit, and Roman Mines. 



Besides these ores of lead, sulphate of barytes, sulphuret of iron, 

 and carbonate oflime are very abundant. 



Stiper Stones. — This dentated and lofty ledge of quartz rock 

 belongs to sandstones of the fifth formation of the previous table*, 

 which have been altered by igneous action, and thrown up into their 

 present highly inclined and broken forms by the eruption of vol- 

 canic rock, lines of which are pointed out both on the western and 

 eastern faces of the ridge, and some of which it is presumed lie con- 

 cealed beneath it. 



To the west and south of the above district small portions of trap 

 are noticed at Nantcribba, Montgomery, and at Heblands near 

 Bishop's Castle. 



Breiddin Hills. — These hills are divisible into ridges running 

 from east-north-east to west-south-west, which, although parallel to 



* See the Table. 

 2G2 



