Older Palcvozoic Succession of the Duddon Estuary. 001 



outcrop 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 GO | Volcanic 



Harrath Tuffs 100 )■ group, 



Middle Tuffs 300 | 6o0 feet. 



Dog Crag Tuffs 50 J 



Mottled shale 100 



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, indis- 

 tinguishable 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 np 

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

 the upper part, felsite. The rhyolites are considered to be sub- 

 stantially contemporaneous. The thin andesitic Upper 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 andesine-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 Couiston 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 fos- 

 siliferous limestone was discovered among the 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 con- 

 clusion that an unconformity exists was confirmed by a trench 

 cuttiug Couiston 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. 



