Volcanic 



group, 



650 feet. 



280 Reports and Proceedings — Geological Sociefi/ of London. 



of several miles, and the alteration is generally less than in other 

 parts of the Lake District. The following succession is described in 

 descending order : — 



Thickness in feet. 



Limestones (Sleddale Group) . . . 100 



Stile End Beds 40 



{unconformity) 



Upper Tuffs 40 



Ehyolites . 



Harrath Tuffs . 



Middle Tuffs 



Dog Crag Tuffs . 



Mottled shale 



Blue shale or (?) Skiddaw Slate — no base seen. 



The blue shale and mottled shale are described ; and it is shown 

 that the latter is identical with the former, except for the addition of 

 lapilli of andesite-glass and slate. Tuff-free bands, indistinguishable 

 from blue shale, are intercalated. Conformity is also proved by 

 mapping and by sections exposing the junction. 



The Dog Crag type is of the same material as the mottled shale, 

 but with little muddy matrix, and passes up into the bedded Middle 

 Tuffs, composed of fine-grained debris ; these in turn pass up into the 

 Harrath type, marked by fragments of variolite, and, in the upper 

 part, felsite. The rhyolites are considered to be substantially 

 contemporaneous. The thin andesitic Tipper Tuffs are only seen in 

 the neighbourhood of Millom. 



The pyroxene-andesites of the district are briefly described. They 

 vary from acid forms with oligoclase in the ground-mass and felspar- 

 phenocrysts, to forms with an andesiue-augite matrix and augite- 

 phenocrysts. They occur sporadically in any horizon from the 

 Skiddaw Slate to the rhyolites, and in many cases are certainly 

 intrusive. The sills metamorphose the Middle Tuffs near their 

 margins into ' halleflintas '. 



It is next shown that the whole succession has been thrown into 

 folds with axes trending north-east and south-west, and now lies in 

 folded sheets with a low dip, though the bedding dips are high. 

 This folding having been determined, it is possible to decide the 

 relationship of the Cuniston Limestone Series to the underlying beds. 

 Near Millom the Upper Tuffs and Stile End Beds are developed. The 

 latter are composed of detrital igneous matter. At Waterblean the 

 Stile End Beds disappear. At Graystone House, near Duddon Bridge, 

 where an important exposure of fossiliferous limestone was discovei'ed 

 among tlie volcanic rocks by Sedgwick, the Upper Tuffs are also 

 absent. On the east side of the estuary mapping shows the limestone 

 lying upon the Dog Crag type, the mottled shale, and the blue shale 

 or andesite. The conclusion that an unconformity exists was con- 

 firmed by a trench cutting Coniston Limestone resting upon 

 undisturbed intrusive augite-andesite. 



The existence of a powerful strike-fault is proved by the position of 

 the Graystone House Limestone and by repetition of the upper part 

 of the volcanic group. 



