THE B0RR0WDALE SERIES AJSTD THE CONISTON FLAGS. 471 



scene of the intense volcanic activity which gave birth to the Bor- 

 rowdale series. 



3. Graptolitic Mudstones. 



Resting directly upon the Coniston Limestone, in every locality 

 where the summit of the latter has been recognized, is a series of 

 dark-coloured Mudstones and grey Shales, which, though of small 

 vertical thickness, are of especial interest from the organic remains 

 which they contain. These beds were originally described by us 

 (Quart. Journ. Geol. Soc. vol. xxiv. p. 296) ; and to them was applied 

 the name " Graptolitic Mudstones," as indicating their general mineral 

 character and the predominant fossils which they yield. Subse- 

 quently, as an alternative local name, the title " Skelgill Beds " was 

 proposed by one of us for these strata, from the farm of High Skelgill, 

 near Ambleside, where they are typically developed (Nicholson and 

 Lapworth, Eep. Brit. Assoc. Bristol, 1875). As before stated, imme- 

 diately above the highest member of the Coniston Limestone these 

 Graptolitic Mudstones come on. The finest sections of the series, 

 however, are to be found on both sides of Long Sleddale, in Skelgill 

 Beck, near Ambleside, in Appletreeworth Beck, and in Swindale 

 Beck, near Knock. 



Many other localities exhibit the same beds ; but they are gene- 

 rally badly exposed, and, from their comparatively soft nature, they 

 often become so far worn down as to be indicated simply by a 

 depression immediately following the outcrop of the limestone. 



In their mineral characters the Graptolitic Mudstones are so well 

 marked that they may be recognized by this alone, apart from the 

 detection of their characteristic fossils. They consist of dark-coloured, 

 often nearly or quite black Mudstones, which are sometimes anthra- 

 citic, the joints of which are characteristically iron-stained. These 

 dark Mudstones are replete with beautifully preserved Graptolites, 

 and alternate in successive bands with lighter and darker grey or 

 even sometimes greenish shales, both the light and dark bands being 

 more or less cleaved. Annexed is a diagrammatic sketch (fig. 3) 

 showing the succession of the strata at Skelgill, where the Graptolitic 

 Mud-stones are admirably exhibited. 



In our earlier researches in the Graptolitic Mudstones we devoted 

 ourselves principally to the black bands containing Graptolites, a 

 large number of species of these organisms being described by one 

 of the present writers from this group (Nicholson, Quart. Journ. Geol. 

 Soc. vol. xxiv. p. 521). More recently an examination has been 

 made, in greater detail, of the grey bands which interstratify the 

 dark-coloured graptolitic layers, with the gratifying result that these 

 have been proved to contain a considerable number of fossils of 

 higher organization than Graptolites. We append a list of the more 

 important species of Graptolites, and of the other fossils at present 

 known as occurring in this series. 



Q.J. G. S. No. 131. 2 1 



