\ 
Keegan: The Rocks of Patterdale (Ullswater). : 
mass, an andesite more definitely characteristic than the one 
above described. The porphyritic constituents have been crushed 
out of all regular shape, the larger ones being’ mostly changed to 
bright green chlorite, and all more or less dusty through 
apparently on considerable portions of the ground-mass 
which surrounds them. ‘his ground-mass is exceedingly 
remarkable ; it is brown, and plentifully bestrewn with granules 
of oxides of iron, but the felspar laths and microlites are clearly 
and abundantly seen, although rather irregular in size and 
shape, with the usual fluxion structure, and all apparently quite 
fresh and unaltered; there is no distinct pseudomorph after 
augite on the slide. A rock from: Angle Tarn Gill shows 
numerous well-formed felspar crystals very much altered, and 
embedded in a ground-mass which is quite dark between crossed 
nicols, owing, no doubt, to an extensive infiltration of iron 
oxides. This rock might be, and doubtless has been, mistaken 
for an ash; but the unbroken and uncorroded felspars, and some 
symptoms of the presence of microlites in the base, seem to 
prove it to belong to a lava flow. The craggy, fluted, and riven 
aspect of the steeps below Brock Crags betoken the presence of 
lava outcrops; but we will now cross over to the western side of 
the vale. 
A rock on the roadside not far from Brothers Water is fine- 
_ grained, and suggests a structure more basaltic than usual ; and 
the microscopic revelations quite confirm this idea. There are very 
few appearances of porphyritic constituents, and such as there 
-are have quite lost their original contours, being eaten up, as 
it were, by the ‘base.’ The latter consists almost entirely of 
large, lath-shaped crystals of altered felspar, with some small 
prisms of the same; the whole embedded in a dusty and 
granular ground-mass, thickly paved with both large and 
minute grains of oxide of iron. The general structure might — 
hat of i 
extensive metamorphosis renders the correct diagnosis rather — 
difficult. Advancing northwards down the valley, we gradually 
approach a vast projection of steep, dark, and craggy eminences 
crowned with a cone. This is Annstone Crag, an offshoot of — 
St. Sunday Crag; and it may be pronounced to be the most | 
‘signally conspicuous and indubitable development of lava that is_ 
to be seen anywhere in the eastern portion of the Lake District. — 
_ Two sections of this Sa here exposed were prepared, one from 
‘ _ the summit of the mountain, the other from the base thereof. — 
ave ve for the detestable alteration, oe flee a ik ert o 
» 1898. 
