T. C. Cantrill — Coal-boring at Presteign, Radnorshire. 483 



of nodules and two thin bands subordinate to shale, yielded (to quote 

 the original nomenclature) Asaphus caudatus, Calymene variolaris, 

 C. macrophthalma, and Isotelus. 



For the most complete geological description of the district the 

 inquirer must turn to a paper read before the Geological Society of 

 London in May, 1850, by J. E. Davis, 1 apparently only a month 

 before the first issue of the Geological Survey map. The purpose of 

 the author was to show that the limestone of Nash and Presteign 

 is of Wenlock age, as had been stated by Murchison in 1839, and not 

 of Woolhope age, as Sedgwick had surmised as a result of a visit 

 in 1846. Incidentally we gather that on the northern side of the 

 Gorton ridge the limestone formerly quarried at " the old and now 

 abandoned excavations ... at the ' Sandbanks ' " is about 8 feet 

 thick, is highly crystalline, is separated from the Caradoc Sandstone 

 by a few feet of shale, and is overlain by a greater thickness, of 

 Wenlock Shale. He pointed out that the sandstone contains 

 abundant specimens of Pentamerus oblongus, Sow., Atrypa hemispherical 

 Sow., and various species of Orthis. From the limestone of the Sand- 

 banks he recorded only Orthis pecten ?, Dalin., Lingula quadrata ?, 

 Eichw., and Orbicula Forbesi, Lav. He gave a long list of fossils 

 from the Wenlock Shales of the Sandbanks, and remarked that 

 fragments of Bumastus barriensis (Murch.) \_ = Ill<Bnus barriensis~\ 

 occur in great abundance. 



The first edition of the Geological Survey map (56 N.E.), undated, 

 but published probably in 1850, showed the Corton ridge as an 

 anticline of "Caradoc Sandstone", with a band of "Silurian 

 limestone" dipping off its northern foot and succeeded by the 

 Wenlock Shale. On a later edition (dated June, 1850, though 

 probably this date refers to the publication of the first edition) the 

 nomenclature is brought up to date, the term " Caradoc Sandstone " 

 being replaced by " TTpper Llandovery Pock ", while the limestone 

 is definitely referred to as " Woolhope Limestone". 



In 1854 Murchison, 2 in his Siluria, an abridgment of his earlier 

 work, devoted a woodcut to a longitudinal section of the ground 

 lying between Corton and Presteign. He represented the Caradoc 

 [Upper Llandovery] Sandstone or Corton Grit as dipping steeply 

 northward under a group of shales with subordinate courses of 

 limestone, which he named " Lower Wenlock Shale and Woolhope 

 or Lower Wenlock Limestone". He thus tacitly relegated the 

 limestone to an horizon between the Caradoc and the Wenlock Shales, 

 and definitely correlated it with that of Woolhope. He also noted 

 that the Corton Grit is laden with the casts of Pentamerus oblongus. 

 In later editions of the same work s he accepted the separation of the 



if we call it the Presteign Limestone, or the Presteign outcrop of the Woolhope 

 Limestone. The other outcrop, on the southern side of the ridge, is known as 

 the Nash or Nash Scar Limestone. 



1 " On the Age and Position of the Limestone of Nash, near Presteign, 

 South Wales " : Quart. Journ. Geol. Soc, vol. vi, pp. 432-9, with a section, 

 1850. 



2 Siluria, 8vo, 1st ed., 1854, pp. 89, 90, 102, 103. 



3 e.g. in 3rd ed., 1859, pp. 101, 117, 118. 



