BARKER : PETROLOGICAL ^'OTES. 
411 
that of the so-called " saussurite-gabbros." A boulder some distance 
south of High Stacks shows a rather coarsely crystalline admixture of 
a green fibrous amphibole with a dull white felspathic substance. 
Micro. [1054] The slice shows at once that we are dealing with 
a gabbro in which the pyroxene has completely passed over into a 
fibrous amphibole of the kind known as uralite. This gives a pale 
green tint, sometimes almost colourless. Vibrations nearly parallel 
to the fibres give a bluish green, those transverse a paler and yellower 
green. A rather wavy fibrous structure is common, but some of the 
cross-sections show^ the proper prismatic cleavage of hornblende. 
Most of the felspar is converted into a clotted, opaque product with 
abundant secondary quartz ; but the few scraps which remain unde- 
stroyed show fine twin-lamellation with moderate extinction-angles, 
and are probably labradorite. 
This rock seems to be identical with some of the " saussurite- 
gabbros," which have been described from south-western Norway, and 
occur also in the north. There need be no hesitation in referring the 
boulder to that country as its source. 
No. 25 is, with little doubt, another variety of the same group 
of rocks. It is a medium-grained crystalline rock, showing plenty of 
dark-green hornblendes set in a light-coloured felspathic substance, 
evidently much altered. 
Micro. [1049] The hornblende is in section very pale to almost 
colourless. Cross-sections exhibit the usual prismatic cleavage-traces, 
and some of the crystals are tw^inned on the usual law. From the 
general character of the mineral and the manner in which the 
irregular crystal plates penetrate one another, besides the nature 
of the rock as a whole, this hornblende seems to be almost certainly 
the result of alteration of the pyroxene in a rock of the gabbro family. 
Outlines of felspar prisms are occasionally detected, but there has 
been extensive decomposition, and much of the rock consists of 
secondary minerals, especially epidote grains and calcite, with some 
quartz. There is a fibrous, colourless hornblende, usually fringing the 
larger crystals of the same, but also occurring in matted patches, and 
clearly of secondary origin. Besides these, there are little prisms 
with high refractive index, weak double refraction, straight extinction, 
