1870.] | NICHOLSON—LOWER GREEN SLATES AND PORPHYRIES. 605 
Hardly any traces of ash-beds can be discovered ; and the series here 
consists of a succession of traps, most of which are highly por- 
phyritic. 
The general sequence of beds in the 
Vale of St. John is indicated in the an- 
nexed 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. 
Ss. 
Armboth Fell. 
V. Lower portion of the Green-slate 
Series in Matterdale. 
Eastwards from the Vale 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 Threl- 
keld Common from Flaska Moor, to- 
wards the head of the stream the 
Skiddaw Slates are seen to be suc- 
ceeded to the south by a mass of fel- 
spathic 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 ex- 
posed 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 
ear Armboth. 
Low Bank. 
s. Place of the Borrowdale Slates. 
Felstone-dyke n 
S 
2. 
Smeathwaite bridge. 
RETREAT 
p of the Green-slate series. 
ale of St. John. 
Naddle Fell. 
6. Lowest tra 
Nes 
Chapel 
Low of St. 
Rigg, John. 
tt od 
Syenite of the V 
HK 
xs 
* 
Beat 
Fig. 3.—Section from Threlkeld Station to Armboth. Distance five miles. 
: ai t 
a. Skiddaw Slates. 
Mm. 
Keswick 
