6 Keegan: The Rocks of Patterdale (Uliswater). 
the rocks which break out at ee intervals there will be found 
amply suitable for the same purpos 
f the two principal varieties of the eruptive rocks which, as 
aforesaid, compose the visible areas of the Patterdale mountains, 
we will commence with a description of the lavas. Somewhat 
about six sections of these from different points have been pre- 
pared; and the first feature one notices about them, even with 
the naked eye, is that they are markedly dissimilar one from 
another. There is a well-defined bed of lava on the north-western 
slope of Silver Hill, whence it strikes in a rather broadish sheet 
or dyke in a south-westerly direction, straight into Ullswater. 
Two sections from this have been prepared for the microscope. 
The structure is decidedly porphyritic, with a ground-mass which 
has not apparently been entirely converted into a felsitic base. 
The large or ‘ porphyritic’ crystals still retain for the most part 
Ce their original crystallographic outlines. The larger of these have 
ae been felspar, and are still comparatively unaltered, showing 
Be only thin steeaies and fragments of a pale green chlorite, and 
a sundry patches of oxide of iron. There are some pseudomorphs 
of pale chlorite after augite, one or two of them still retaining 
the exact octagonal outline of the usual cross sections of the 
latter mineral. The ground-mass presents an appearance similar 
to that of a fresh, unaltered andesite, but the characteristic 
; felspar laths are not readily discernible with a low objective in 
ordinary light ; under polarised light, however, or by using a 
higher magnification, a large number of short, stumpy microlites 
and sections of the same are seen strewn over a matrix of light- 
coloured glass, which is streaked and patched with chlorite 
akelets, and small granules of epidote, etc. On the whole, 
while this rock is clearly an andesite, it has evidently been. 
mation is not strikingly obvious. There is a very fine-grained — 
rock from a quarry above Bleawick (Place Fell) which is wholly — 
composed of a ground-mass closely similar to the above, and 
without any porphyritic crystals ; it seems connected with two 
narrow bands of lava which strike north-west from near the head 
_ Ullswater. Following the course of the mountains south- 
ards, we arrive ata point above Dubhow Farm, where a grisly 
ated of vertical rock attests the presence of an intrusion of 
lava. A section of this rock reveals it to be very similar to some 
a of the augite-andesites in the vicinity of Derwentwater. It is a 
__ greenish-tinted rock, with large crystals visible to the naked eye. _ 
‘Unde der =e ee it is. ‘Seen 1 fo tee as apo the ground-— 
somewhat metamorphosed, but the tendency towards calcite for- : 
Nae, ‘ea 
