178 T. G. BONNEY AND F. T. 8, HOUGHTON ON MICA-TRAPS 
grey in colour, of rather decomposed aspect. The felspathic ground- 
mass 1s crowded pretty thickly with minute scales of mica, with a 
rather silvery lustre. The rock is traversed here and there by thin 
veins of quartz. 
Microscopic. A cryptocrystalline felspathic ground-mass, with a 
general resemblance to those from Helm Gill. Much brown mica 
(some of the smaller plates of a green colour), some apatite, several 
grains of iron peroxide (? ilmenite), and a considerable number of 
crystals and grains resembling those in the lower Helm-Gill rock, 
and probably pseudomorphs after augite. Calcite is undoubtedly pre- 
sent in a vein, and there is probably some disseminated dolomite. 
The rock is probably a minette-felsite. The dyke is a narrow one, 
and is intrusive in Coniston Limestone. 
(16) Wattle Gill, Westerdale. 
Characters.—Macroscopic. A compact dark rock, containing a 
quantity of black mica, generally in small crystals, rarely exceeding 
0-1 inch diameter, and some scattered crystals, occasionally a little 
longer, of a pale-grey colour. Weathers brown. 
Microscopic. Very similar to those of the rock from Uldale Head, 
except that extremely little, if any, of the base remains in a glassy 
condition. A separate description is hardly necessary. Here also 
there is variety in the pseudomorphous products replacing the augite 
erystals and grains. One which affords a perfectly characteristic 
8-sided section, with the usual rectangularity of the alternate sides, 
is mainly occupied by a pale olive-brown, hardly dichroic mineral, 
which with crossed Nicols appears an aggregate of several minute 
minerals. In the majority, however (which in form are less cha- 
racteristic), dolomite appears to predominate. It contains numerous 
enclosures, three or four being brown mica, and some, apparently, 
portions of the base, containing (felspar?) microliths. 
The dyke is a narrow one, intrusive in Coniston Limestone, and is 
probably kersantite-porphyrite. 
(17) Dyke from the upper part of Westerdale. 
Characters.—Macroscopic. A compact, dull greenish-grey rock, 
with some darker specks, and a great number of mica-scales, almost 
too minute to be visible to the unaided eye, of silvery aspect, so that 
it is by no means a conspicuously micaceous rock. It is evidently 
much decomposed, and weathers a rusty brown. 
Microscopic. There has probably been a glassy base crowded with 
microliths of felspar, augite, mica, and ferrite ; but the present condi- 
tion of the rock makes it difficult to speak confidently. In this are 
numerous small crystals of biotite, rather full of enclosures, often 
with interstitial calcite (?), also, possibly, large grains of some white 
mica, iron peroxide, and numerous crystalline grains of either augite 
or hornblende, chiefly replaced by viridite (serp. var.), and some cal- 
cite or dolomite. Some colourless crystals may be pseudomorphs 
after felspar, but they have rather the aspect of a micaceous or pyr- 
oxenic mineral. 
The general aspect of the rock suggests affinities with the basic 
group, so that it probably is a kersantite-porphyrite. It forms a 
