ON THE STOCKDALE SHALES. 657 



dale Shales under the term " G-rey Grits." Both these sets of 

 deposits are included as a subdivision of the Coniston Flags, and the 

 Mudstones are considered to rest conformably upon the Coniston 

 Limestone, and are referred by the authors to the Bala. 



"We append a brief abstract of the views expressed in various 

 papers which have appeared subsequently to the one above referred 

 to, and which treat specially of the Stockdale Shales. 



1868. " On the Graptolites of the Coniston Flags," by H. A. 

 Nicholson (Q. J. G. S. vol. xxiv. p. 521). 



Alters the term " Graptolitiferous Mudstones " to " Graptolitic 

 Mudstones," and describes many Graptolites from these beds. 



1868. ' An Essay on the Geology of Cumberland and Westmore- 

 land,' by H. A. Nicholson. 



The Stockdale Shales included as a member of the Coniston Flags. 

 Fossil lists given. Age considered as between that of Bala Lime- 

 stone and that of Lower Llandovery. 



1872. " Migrations of the Graptolites," by H. A. Nicholson (Q. 

 J. G. S. vol. xxviii. p. 217). 



Gives list of species from the " Graptolitic Mudstones." 



1872. " Memoirs of the Geological Survey." Explanation of 

 Quarter Sheet 98, N.E., by Messrs. W. T. Aveline and T. M^K. 

 Hughes. 



First use the term " Stockdale Shales," and separate them from 

 the Coniston Flags : divide them into a lower portion, *' Grapto- 

 litic Mudstones," and an upper, " Pale Slates." Give the lithological 

 characters of each, and a list of fossils from the " Graptolitic Mud- 

 stones" of Holbeck Gill (=Skelgill), near Ambleside. Refer them 

 to Upper Silurian. 



1872. " On the Silurian Eocks of the English Lake District," by 

 Prof. H. A. Nicholson (Proc. Geol. Assoc. 1872, p. 105). 



Discusses age of " Graptolitic Mudstones " ; abandons view that 

 they belong to Coniston Flags, and refers them to Lower Silurian, 

 and considers them conformable with beds above and below. 



1872. " On the Continuity and Breaks between the various divi- 

 sions of the Silurian Strata of the Lake District,'" by W. T. Aveline 

 (Geol. Mag. vol. ix. p. 441). 



Considers slight unconformity to exist between Coniston Lime- 

 stone and Stockdale Shales : refers latter to Upper Silurian, and 

 correlates them with Tarannon Shales of North AYales. 



1875. " On the central group of the Silurian series of the North 

 of England," by H. A. Nicholson and C. Lapworth (Eep. Brit. Assoc. 

 1875, p. 78). 



Use the term " Coniston Mudstone series " for the Stockdale 

 Shales, and suggest the term " Skelgill Beds" for the " Graptolitic 

 Mudstones," and that of " Knock Beds " for the Pale Slates, and 

 correlate the entire " Coniston Mudstone Series " with the Lower 

 and Upper Llandovery and Tarannon Shales of North Wales. 



1876. " Absence of Llandovery Rocks in the Lake District," by 

 W. T. Aveline (Geol. Mag. dec. ii. vol. iii. p. 282). 



Again correlates Stockdale Shales with Tarannon Shales. 



