SILURIAN. 



107 



Mr. A. Marston has described sections of these beds consisting 

 of olive shales, which were exposed on the Shrewsbury and Hereford 

 Railway at the Tin Wills, near Downton, and near Onibury.^ 

 These shales rest on grey micaceous sandstones (Downton Sand- 

 stone). (See Fig. 15.) 



SILURIAN. 



2.— LAKE DISTRICT, ETC. 



The Silurian rocks of the Lake District, etc., have been divided 

 as follows : — 



Upper 



Coniston 



Group. 



Kirkby Moor Flags. 

 Bannisdale Slates. 



Coniston Grits. 

 Coniston Flag-s. 



Stockdale Shales. 



Pale Shales or Slates. 

 Graptolitic IMudstones. 

 Basement Bed (Austwick Conglomerate, etc.). 



The relations of the rocks were first determined by Sedgwick ; 

 while the detailed work of the Geological Survey was. carried out 

 chiefly by Mr. W. T. Aveline, Prof. Hughes, and Messrs. J. G. 

 Goodchild and E. J. Hebert.^ 



Basement Bed of the Silurian. 



At Austwick, near Settle, in the Craven district, a calcareous 

 conglomerate occurs at the base of the Silurian system, resting 

 unconformably on the Bala Beds. This basement-bed, as before 

 mentioned, is regarded by Prof. Hughes as the equivalent of the 

 Corwen Grits.^ (See p. 85.) The bed occurs beneath the Grapto- 

 litic Mudstones near Sedbergh, and is about 15 feet thick. 



Certain calcareous and gritty bands forming the base of the 

 Silurian rocks occur at Skelgill, at Pullbeck near Ambleside, and 



1 G. Mag. 1870, p. 409. 



^ See also Dr. H. A. Nicholson, Essay on the Geology of Cumberland and 

 Westmorland, 1868; Sedgwick, Geol. Lake District (Letters to Wordsworth), 

 1843 ; and various papers by Prof. R. Harkness. 



^ Proc. Cambridge Phil. Soc. iii. 67 ; G. Mag. 1867, p. 352. 



