1868.] NICHOLSON — coniston-flag gr,vptolites. 521 



15. On the GRArxoLixEs of the Coxiston Flags ; with Notes on the 

 British Species of the Genus Graptolites. By Henry Alleyne 

 Nicholson, D.Sc, M.B., F.G.S. 



[Plates XIX. and XX.] 



The Silurian series of the north of England is composed of the 

 following groups in ascending order : — 1, the Skiddaw Slates ; 2, 

 the Green Slates and Porphyries ; 3, the Coniston Limestone ; 4, 

 the Coniston Flags ; 5, the Coniston Grits ; and, 6, the Ludlow Hocks. 

 Of these, the Skiddaw Slates contain a large and remarkable series 

 of Graptolites, which are mostly identical with those of the Quebec 

 group of America (see a paper by the author, Quart. Journ. Geol. 

 Soc. vol. xxiv. p. 125). The Green Slates and Porphyries, and the 

 overlying Coniston Limestone, with the exception of a fragment of a 

 Diplograpsus from the former, have hitherto proved entirely barren 

 of Graptolitic remains ; and the same is true of the Ludlow group. 

 The Coniston Flags, however, contain, as shown by Professor Hark- 

 ness and myself, a very extensive and varied Graptolitic fauna, 

 which it is the object of the present paper to describe. 



As to the limits and age of the Coniston Flags, as well as their 

 relation to the underlying limestone, considerable diversity of opinion 

 exists, almost the only point in which all observers are agreed 

 being that the Flags form a single natural group with the super- 

 jacent Grits. For my present purpose, however, it will suffice 

 merely to indicate the different opinions which are held upon the 

 subject. By Professor Sedgwick the Coniston Flags were held to be 

 everywhere conformable to the Coniston Limestone ; and he at first 

 regarded them as of Wenlock age, a view which he subsequently 

 modified so far as to refer them to the summit of the Lower Silurian 

 division, whilst he placed the Grits at the base of the Upper Silu- 

 rians. By Mr. Hughes, again, the Coniston Flags are believed to be 

 unconformable to the Coniston Limestone, and to form, with the 

 Grits, the base of the Upper Silurian series of the north of England 

 (see Geol. Mag. vol. iv. p. 346). Lastly, it is believed by Professor 

 Harkness and myself that the Coniston Flags include all the beds 

 between the summit of the Coniston Limestone proper and the base 

 of the Coniston Grits, that the flags are strictly conformable to the 

 limestone, and that their age is Lower Silurian (see Quart. Journ. 

 Geol. Soc. vol. xxii. p. 480 & vol. xxiv. p. 296). 



Proceeding upon this last-mentioned view, the Coniston Flags are 

 found to consist of the three following chief subdivisions in ascend- 

 ing order : — 1, black mudstones or shales, occasionally almost an- 

 thracitic, alternating with unfossiliferous grey grits, which become 

 more developed as we ascend ; 2, cleaved flags, which are largely 

 worked for industrial purposes ; and, 3, " sheer-bate" flags, in which 

 the cleavage and the bedding coincide with one another. The 

 black madstones or shales of the lowest subdivision are richly 

 charged with Graptolites in a state of excellent preservation ; and it 

 is here that the greatest number of genera and species are found. 

 To this portion of the series belong the Graptolite-beds of Mosedale 



