487 
NOTES ON THE IGNEOUS ROCKS OF THE ENGLISH LAKE DISTRICT. 
BY ALFRED HARKER, M.A., F.R.S., F.G.S. 
I. — The Ordovician Volcanic Series. 
This series is divisible stratigraphically and petrographically 
into several distinct groups, the distribution of which in the district 
has been indicated by Mr. Marr.^ 
(a) Falcon Crag Andesite Group. — These rocks are found chiefly 
in the country south of Keswick and eastward to the St. 
John's Yale. They are pyroxene-andesites, and thin slices 
show under the microscope sometimes hypersthene (con- 
verted to bastite), sometimes augite, sometimes both. To 
the eye the rocks are pale greenish to dark grey, with a 
compact ground-mass, usually containing scattered minute 
porphyritic felspars, or more rarely abundant crystals up 
to J inch in length. Many of the flows are amygdaloidal. 
There are rare flows of more basic lavas, besides some tuffs. 
(b) Eycott and Ullswater Basalt Group. — The most widely dis- 
tributed group of all. The basalts, like the andesites, often 
contain altered hypersthene ; they are sometimes rather 
rich in magnetite, but olivine does not occur. These rocks 
are usually darker and denser than the andesites, but a 
discrimination is not always possible in the field. Part 
of the rocks are porphyritic, and in some there are con- 
spicuous crystals of felspar (bytownite or labradorite) which 
on Eycott Hill reach a diameter of an inch or more. Amyg- 
daloidal varieties are found. Basic tuffs are sometimes 
intercalated among the lavas, and in some places there are 
andesitic flows included in this group. 
(c) Scawfell Tuff and Breccia Group, with Kentmere-Coniston 
Slate-Band. — This group presents itself under two different 
phases. (1) In the central mountains it consists mainly of 
*Proc. Geol. Assoc., 1900, Vol. XVI., pp. 453-459, with map (Plate XIII.) 
