between the JBorrowdale Rock* and Coniston Flags. 393 



The : '* Dufton Shales " are a well-marked, but locally distributed 

 group of muddy deposits, especially well developed in the Silurian 

 area underlying the Cross-Fell range, where they are seen in four 

 principal exposures ; and their thickness probably exceeds 300 feet. 

 They are richly fossiliferous, the fossils being generally of Bala 

 types ; and they may be regarded as forming, palaeontologically, the 

 base of the Coniston Limestone. The fossils sometimes occur in 

 ash-beds ; and the continuance of these conditions leads the authors 

 to believe that there was no break between these shales and the 

 underlying Borrowdale rocks. 



The " Coniston Limestone " has long been recognized as the best- 

 defined division of the Lower Silurian rocks of the north of England. 

 Its range and characters, and those of the associated shales in 

 different localities, are indicated by the authors ; and from the con- 

 tained fossils, they refer it, at least approximately, to the horizon of 

 the Welsh Bala Limestone, whilst they regard it as the precise equi- 

 valent of the Lower Silurian of Portraine (co. Dublin), and of that 

 of the Chair of Kildare, both of which are of Bala age. 



The " Graptolitic Mudstones " overlie the Coniston Limestone 

 wherever the summit of the latter is to be seen. Besides Grapto- 

 lites, they contain many other fossils, including Corals, Brachiopods, 

 Cephalopods, and Crustaceans ; and from the consideration of the 

 whole fauna, the authors are led to believe that the position of these 

 deposits must correspond either with the highest beds of the Bala 

 series, or with the lower portion of the Llandovery group. In their 

 opinion, there is perfect conformity between the Mudstones and the 

 underlying Coniston Limestone. They regard the Graptolitic Mud- 

 stones as constituting a definite geological horizon of more than 

 local importance, as they have been recognized in Ireland, Sweden, 

 Carinthia, and Bohemia. 



The Graptolitic Mudstones are succeeded by the " Knock beds," 

 so called from their great development in Swindale Beck, near 

 Knock. Wherever they occur they consist chiefly of pale green 

 fine-grained slates, very ashy in appearance, and presenting many 

 dendrites, and frequently crystals of cubic pyrites. There is no 

 evidence of unconformity between them and the underlying Mud- 

 stones. The former contain scarcely any fossils. They are directly 

 surmounted by the " Coniston Flags," representing the Denbighshire 

 Flags of North Wales, which have been shown to be of Upper Silu- 

 rian age. Hence the authors conclude that the Knock beds must 

 be either the basement series of the Upper, or the summit series of 

 the Lower Silurian, or else a group of passage-beds between the 

 two. The palaeontological evidence is insufficient to settle the point ; 

 but it tends to show that the Knock beds are at the base of the 

 Upper Silurian— an opinion which is corroborated by their litholo- 

 gical resemblance to the Tarannon slates of Wales. 



The paper concluded with an appendix on the Irish rocks re- 

 ferred to above. 



2. " On a new Area of Upper Cambrian Rocks in South Shrop- 



