464 R. HARKNESS AND H. A. NICHOLSON ON THE STRATA BETWEEN 



Ci/bele verrucosa, fflomus Bowmanni, and Lichas laxatus, can leave no 

 doubt as to the correctness of the inference that these rocks belong to 

 the Bala or Caradoc age. The presence of what appear to be unequi- 

 vocal ashes which contain some of these fossils high up in the series at 

 Swindale also deserves attention as showing that the volcanic forces 

 which gave rise to the ashes and lavas of the Borrowdale group still 

 maintained an intermittent activity during the deposition of the 

 Dufton Shales. There would thus appear to have been no break of 

 continuity between these shales and the underlying Borrowdale 

 rocks — a conclusion which is further borne out by the substantial 

 identity between the fossils of the Dufton Shales and those of the 

 Style-End Grassing beds. 



The annexed section (fig. 1) exhibits the stratigraphical relations 

 of the Dufton Shales in Swindale Beck, where, as before stated, 

 they are very well exposed. 



Fis. 1.- 



-JT.INTJE 



-Sketch Section of the Strata in Swindale Beck, near Knock. 

 (Length rather more than half a mile.) 





s.sw 



a. Ashes belonging to the Borrowdale series 



c. Coniston Limestone. 



e. Knock beds (green and purple slates). 



/. Black flags with Monographs colon us, Barr., probably Coniston Flags. 



b. Dufton Shales. 



d. Graptolitic mudstones. 



2. Coniston Limestone. 



The " Coniston Limestone," notwithstanding its comparatively 

 small vertical extent, has long occupied the position of being the 

 best-defined and most universally recognized of all the divisions of 

 the Lower Silurian series of the north of England — a position which 

 it owes to its easily recognized lithological characters, and to the 

 number of organic remains which it has yielded. It is unnecessary 

 here to recapitulate the geographical range of the Coniston Lime- 

 stone. Its main line of outcrop crosses the Lake-district in a direc- 

 tion from S.W. to X.E., running from Millom on the one hand to 

 Snap Wells on the other. It is more or less developed in Raven- 

 stonedale,Dentdale. the Sedbergh valley, near Ingleton, in Ribblesdale, 

 at Ireleth, at High Haulme. in Furness. and at various points in 

 the Lower Silurians which lie to the south-west of the Cross-Fell 

 range. 



Lithologieally the term " Coniston Limestone '' is somewhat mis- 

 leading, as it is never wholly calcareous in its composition, and the 

 calcareous element is occasionally almost wanting. In its most 

 typical form, as seen in its range between Long Sleddale and 

 Broughton Mills, in Furness, the Coniston Limestone consists of 



