﻿234 Heports and Proceedings-r- 



F.E.S.E., F.G.S., Professor of Natural History in. the University of 

 St. Andrews. 



The object of this paper was the investigation of the strata 

 between the great volcanic series of the Lake-district, the Borrow- 

 dale rocks, and the sedimentary rocks called Coniston Flags by 

 Prof. Sedgwick. The Borrowdale series, the Green Slates and 

 Porphyries of Sedgwick, are underlain by the Skiddaw Slates, 

 forming the base of the Silurian series, and equivalent in age to the 

 Arenig rocks of Wales, according to their fossil contents. The 

 Borrowdale rocks consist of ashes and breccias, alternating with 

 ancient lavas, and are partly subaerial, partly submarine. They 

 contain no fossils except in a band of calcareous ashes near the 

 summit of the group, which is followed by the Conistone Limestone, 

 with or without the intervention of a bed of trap. The fossils are 

 of Bala types. Sometimes this band is recognizable, with no traces 

 of fossils except cavities filled with peroxide of iron. The authors 

 regard this as proving the prevalence of volcanic activity in the 

 Lake District up to the later portion of the Bala period. 



The deposits specially discussed in the paper sent, lie, apparently 

 quite conformably, upon the Borrowdale rocks, and are grouped by 

 the authors as follows, in ascending order : — 



1. Dufton Shales. 



2. Coniston Limestones and Shales. 



3. Graptolitic Mudstones or Skelgill Beds. 



4. Knock Beds. 



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

 grou]D 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, palaeontologieally, 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 



