I08 SILURIAN. 



at Appletreeworth Beck near Coniston. Prof. Hughes has pointed 

 out that the Graptolitic Mudstones and their basement beds rest 

 on different parts of the Cambrian series ; at Skelgill on the 

 Coniston limestone bands, and near Coniston on the Ashgill 

 Shales.^ 



Mr. J. E. Marr has remarked that " Not only is there a palason- 

 tological break between the Ashgill Shales and what has been 

 taken as the basement bed of the Silurian ; but whereas in the 

 Ashgill Shales and underlying beds we get a group of fossils 

 agreeing in all respects with those of the Cambrian series of other 

 districts, in the beds above the Ashgill Shales we find a well- 

 marked Silurian fauna, which will probably be largely added to in 

 future." ^ Fai'ositcs fibrosus, Strophomena, Orthis, and Mcristclla crassa 

 occur in this Basement-bed. 



STOCKDALE SHALES. 



The Stockdale Shales were so termed by Mr. W. T. Aveline, 

 from their occurrence at Stockdale, east of Ambleside, between 

 Shap Fells and Windermere. 



The beds consist of pale-grey and purple shales, passing down 

 into black mudstones and shales with Graptolites, and containing 

 calcareous grit or conglomerate at the base. They are subdivided 

 as follows : — 



2. Pale Shales ( = Tarannon Shales). lo to 450 feet. 

 I. Graptolitic Mudstones. 30 feet. 



The Graptolitic Mudstones were described in 1868 by Prof. 

 Harkness and Dr. H. A. Nicholson.^ They were formerly included 

 with the Coniston Flags, and termed the Coniston Mudstones. 

 Subsequently the name " Skelgill Beds " was applied to them by 

 Messrs. Nicholson and Lapworth, from the farm of High Skelgill, 

 near Ambleside, where the rocks are well exposed.* 



In the Lake District certain black shales are seen beneath the 

 Graptolitic Mudstones at Spengill, Ashgill, etc. (See p. 83.) Mr. 

 J. E. Marr has obtained one Crinoid and a species of Strophomaia 

 from them.^ 



The Graptolitic Mudstones are dark-coloured and often black mud- 

 stones, sometimes anthracitic, alternating with grey and greenish 

 shales, and graduating upwards into the Pale Shales or Slates. 

 The dark mudstones are full of Graptolites. The beds are seen 

 at Spengill, Skelgill, Long Sleddale, Torver Beck and Swindale 

 Beck ; near Knock ; and again in the neighbourhood of Sedbergh, 

 in Yorkshire. They yield the Graptolites Diplograptus, Rastrites 



1 Q. J. xxxiii. 483. 



2 Q. J. xxxiv. 8S0. See also Q. J. xxxvi. 281. 



3 Q. J. xxiv. 297. 



* Brit. Assoc. 1875. See also Q. J. xxxiii. 471 ; P. Geol. Assoc, iii. in. 



* Q. J. xxxiv. 877. 



