STOCKDALE SHALES. IO9 



peregrinus, Mo7iograptiis argentetis (Argenteus-mudstones) ; also Pha- 

 copsMusheni?, Encrinurnsvariolaris, Cheiruriis bimucronatus, Trinucleiis 

 fi?nbriatus, Leptcsna quinquccostata, Endoceras proteiforme, Orthoceras, 

 and Sphccronitcs piinctatus. 



While some of the Graptolites, excepting Monograpfiis, are of 

 Upper Cambrian or Ordovician types, yet the more highly organized 

 fossils link the beds to the Silurian system, with which also they 

 are physically connected. Mr. W. T. Aveline has observed that 

 the beds rest unconformably on the Coniston Limestone ; ^ and 

 in the Sedbergh district they rest on the Trinucleiis and Strophomena 

 (Ashgill) Shales. The beds were, however, placed with the Upper 

 Cambrian or Ordovician by Messrs. Harkness and Nicholson, ex- 

 clusively on palteontological grounds. 



Dr. Nicholson and Prof. Lapworth have described certain pale- 

 green fine-grained slates developed at Swindale Beck near Knock, 

 under the name of Knock Beds. They resemble the Tarannon 

 Shales, and occur beneath the Coniston (Broughton Moor) Flags. 

 Species of Oiihis and Discina and JMonograptiis priodon are met 

 with in the beds. They were regarded by Prof. Harkness and Dr. 

 Nicholson as the base of the (Upper) Silurian of the Lake District, 

 but the beds graduate downwards into the Graptolitic Mudstones.- 



The Stockdale Shales being comparatively soft, their occurrence 

 is generally marked by a low tract of ground. 



Certain soft shales, formerly worked up into slate-pencils, occur 

 at the old Pencil Mill at Cronkley, in Teesdale. These resemble 

 the Stockdale Shales, according to Messrs. W. Gunn and C. T. 

 Clough, and are probably Silurian in age.^ Silurian shales (of 

 doubtful age) have also been noted near the head of the Rede- 

 water in Northumberland.* Silurian rocks, consisting mainly of 

 shales, with beds of grit and conglomerate, occur in the Cheviot 

 district. They rise up in places to form high ground, and are 

 highly inclined and sometimes vertical, being much folded. (See 

 Fig. 16.) Graptolites have been met with in the beds, and they 

 may belong to the Wenlock or Upper Coniston Series. 



Representatives of the Graptolitic Mudstones are recognized in 

 the Dee Valley by Mr. J. E. Marr.* 



1 G. Mag. 1872, p. 442. 



2 Brit. Assoc. 1875 ; Q. J. xxxiii. 477. 



3 Q. J. xxxiv. 27 ; J. R. Dakyns, Geol. and Polyt. Soc. W. Riding, 1877. 



* G. A. Labour, Geology of Northumberland, p. 46. See also J. Nicol, Q. J. 

 iv. 195. 



* Q. J. xxxvi. 278. 



