Page:Quarterly Journal of the Geological Society of London, vol. 26.djvu/837

 Hardly any traces of ash-beds can be discovered ; and the series here consists of a succession of traps, most of which are highly porphyritic.

The general sequence of beds in the Vale of St. John is indicated in the annexed section (fig. 3), from which it will be seen that the great slate-band of Honister and Borrowdale has now almost completely thinned out, its place being taken by bedded traps. V. Lower portion of the Green-slate Series in Matterdale.

Eastwards from the Yale of St. John the lower beds of the Green-slate series maintain much the same characters, the absence of any well-marked and conspicuous band of slates still holding good. No continuous and complete section, however, can be obtained.

If we follow up a stream known as Mosedale Beck, which divides Threlkeld Common from Flaska Moor, towards the head of the stream the Skiddaw Slates are seen to be succeeded to the south by a mass of felspathic greenstone, which forms the striking eminence known as Wolf Crags, and which constitutes the base of the Green-slate series. Still further to the west, in the course of Trout-beck Beck, about a mile to the south of Troutbeck village, the base of the Green Slates is found to succeed the Skiddaw Slates in the form of a greenish-grey felspathic trap, in part very ashy, and decomposing very readily. This is followed by ash-beds of small thickness ; and these in turn are surmounted by a great mass of porphyritic greenstone. Between this point and Ulleswater no beds are exposed except detached masses of trap, the best section of which is afforded by Aira Beck. From Thorneythwaite by Dockwray, and in the course of Aira Beck itself, no slates or ash-beds are visible ; but there is a constant succession of traps. These vary much in character, but are mostly highly porphyritic, containing numerous crystals of white or orange felspar, and generally a good deal of hornblende. Before reaching Ulleswater, however, on the southern

Fig. 3.-Section from Threlkeld Station to Armboth. Distance five miles.

a. Skiddaw Slates. b. Lowest trap of the Green-slate series. s. Place of the Borrowdale Slates. m. Syenite of the Vale of St. John. n. Felstone-dyke near Arnboth.