412 
HARKER : PETROLOGICAL NOTES. 
and longitudinal cleavage-traces, which must be referred to zoisite. 
All these appearances are such as are found in the "saussurite- 
gabbros." 
Of the numerous examples of gneissic rocks, o)ily two or three 
have been specially noticed, since these do not offer much hope of 
precise determination of then- sources. No. 33 is a dark, fine-grained 
rock, which shows abundant little glistening flakes of mica, arranged 
parallel to a definite plane, while a lens enables us to detect in addi- 
tion some black hornblende. The rock is a horublende-biotite- 
gneiss of fine texture. 
Micro. [1051] The slice has a fresh appearance, showing little 
flakes of brown biotite and green hornblende, set in a clear, finely- 
crystalline ground. As in many other metamorphic rocks, this 
granular gTOund-mass is clear enough for quartz ; but on closer 
examination many of the grains show twinning and even twin- 
lamellation, and there can be no doubt that much of the mass is of 
felspar. Some more or less clear patches, with rather gi'anular 
structure, seem to represent felspar crystals, porphyritic in the 
original rock, but now completely replaced. Ragged crystal-grains 
of magnetite must, from their manner of association with the 
coloured mineral, be also secondary. The rock presents an extremely 
close resemblance to some of the highly metamorphosed volcanic 
agglomerates in contact with the Shap granite in Westmorland, 
and this is the nearest possible locality for its origin : but we cannot 
exclude the possibility of the rock being a dynamo-metamorphic 
product and having its home in Norway. 
A large boulder from south of High Stacks is a typical horn- 
blende-gneiss, showing white felspathic and dark hornblendic bands, 
half-an-inch or more in thickness. 
Micro. [1053] The parallel structure is not apparent in the 
slice. Zircon and apatite occur as the earhest-formed minerals. 
The hornblende is deeply coloured and highly pleochi'oic, giving 
colours varying from intense green, almost opaque, to a rather 
yellowish brown. The felspar is mostly decomposed, but appears 
to have been orthoclase. The quartz is partly interstitial, but 
largely in the form of rounded grains enclosed in the hornblende. 
It shows the " strain-shadows" indicative of mechanical forces. 
