So UPPER CAMBRIAN (ORDOVICIAN). 



rocks are well exhibited, is now generally adopted. The rocks 

 were originally known as the Chloritic Slate and Porphyry. They 

 are overlaid by the Coniston Limestone. 



Mr. Aveline states that, as a whole, the beds consist of lavas and 

 consolidated or altered ashes and breccias, which have been ejected 

 from volcanic vents, and vary in lithological character from thick- 

 bedded coarse breccia to an ash so fine in texture that, when well 

 cleaved, it yields good slates. Hence the name ' Green Slates and 

 Porphyries,' — the term porphyries being applied to the lavas or, 

 locally, even to the altered ashes, in which a porphyritic structure 

 has been developed. The total thickness is estimated at from 7000 

 to 12,000 feet. No fossils have been found in the beds. They 

 probably represent beds from the Llanvirn Series, up to the middle 

 Bala beds. 



The Rev. J. C. Ward stated that alternations of Skiddaw Slate 

 with submarine volcanic deposits occur at the base ; and that there 

 are indications of a gradual passage from submarine volcanic 

 conditions to those of terrestrial and wholly subaerial volcanoes.^ 

 (See sequel.) Mr. W. T. Aveline has also pointed out a conform- 

 able junction to be seen near Bootle.^ Mr. J. R. Dakyns,'^ how- 

 ever, regards the Borrowdale Series and Skiddaw Slates as un- 

 conformable, and so does Prof. H. A. Nicholson.^ The shales 

 overlying the Borrowdale Series, which also contain volcanic 

 rocks, present evidences of local unconformity, inasmuch as 

 they successively overstep various members of that Series, as 

 the junction is followed in a south-westerly direction from 

 Coniston. 



The Borrowdale series occupies the area south of Keswick and 

 south-east of Buttermere, forming, as remarked by Prof. Phillips, 

 along range of mountains parallel to the Skiddaw slates, and those 

 highly picturesque and romantic valleys wherein the lakes of 

 UUeswater, Haweswater, Thirlmere, and Wastwater spread their 

 beautiful waters. The beds may be seen in the Vale of St. John, and 

 Matterdale. Scafell and Helvellyn are formed of them, and they 

 may be seen at Bleaberry Fell and Falcon Crag, near Keswick. 

 In proceeding from Borrowdale, through Langdale to Ambleside, 

 and through Tilberthwaite to Coniston Waterhead, this great and 

 complex series of rocks may be examined in an interesting variety 

 of positions. By a short deviation from Borrowdale, over Sty 

 Head, toward Wastwater, or from Langdale, over Hard Knott, to 

 Eskdale, the granite which breaks into the midst of the series, and 

 sends off porphyritic branches, accompanied by metamorphosed 

 slates, may be well studied. The base of the whole mass, as seen on 

 Derwentwater, about Barrow, is a red or purple mottled argillaceous 

 rock usually regarded as a breccia. The mottled aspect of some of 



' G. Mag. 1S79, p. 50 ; see also the Geology of the Novthern Part of the Lake 

 District. 



2 G. Mag. 1869, p. 382 ; 18S2, p. 441, 



3 G. Mag. 1869, pp. 56, 116. 



* G. Mag. 1869, pp. 105, 167 ; P. Geol. Assoc, ill. io5. 



