106 W. M. Hutchings—Altered Igneous Rocks, Tintagel. 
deal of biotite which is not so arranged, but lies with its flat sides 
in various directions, mostly vertical or highly inclined to the 
_ foliation. It occurs as very numerous individuals with sharp outlines 
and boundaries of tabular crystals. It is all quite fresh and more 
transparent than the other form, and as it has so evidently not been 
in the least degree affected by the rock-movements, it appears to be 
younger than the irregular flakes, and to have been developed since 
the foliation took place. 
Felspar, some of it twinned, is well represented, and there is 
quartz as usual. Rutile is very abundant in some parts of sections, 
as good-sized crystals and grains. The epidote crystals are more 
numerous and larger than in any other specimens examined. Many 
may be picked out with a penknife, and their forms examined with 
a lens, or even with the naked eye; but smaller crystals, not 
perceptible without the microscope, are also plentiful. 
These epidotes lie, by far the greater number, with their long axes 
parallel tothe plane of foliation, lyingin various directions in this plane. 
Hence slides prepared parallel to foliation show hardly any cross-sec- 
tions of the crystals, while such sections predominate in slides prepared 
transversely. Dichroism is moderate, varying from colourless to pale 
yellow. The crystals are mostly very perfect. The usual elongation 
in the direction of the orthodiagonal is so strongly developed that 
the length is mostly very great in proportion to the thickness. The 
forms do not present anything unusual. The ends are in no cases 
bounded by definite planes. Cross-sections parallel to the clino- 
pinacoid, show mostly six-sided forms bounded by the faces 001, 100, 
and 101, but owing to the disappearance in some crystals of the 
faces 100, there are also many rhombic sections. Twinning is 
frequent, both as simple binary twins and as others in which several 
lamelle are inserted between the two main portions. It is developed 
not only in the larger crystals, but also in the the smaller microscopic 
individuals. The occurrence of twinning in small epidotes is stated 
to be not very frequent. 
In the sections of rock now under consideration the epidote has 
not, as a rule, been very much affected by the shearing which has 
developed a very high degree of “flow ” structure in mica, chlorite, 
calcite, iron ores, etc. There are many crystals which do not show 
signs of having suffered any kind of stress or disturbance at all, and 
which would incline one to believe that they had been formed 
subsequently to the foliation of the rock. But there are also others 
which have been broken or bent, some to even an extreme degree, 
though actual separation of fragments is rare; and a large number 
of others which have not been so severely affected still show that 
their internal structure is modified in harmony with the foliation of 
the other minerals, lines of iron ore continuing their straight or 
curving courses right through the epidote sections. Also the layers 
of mica, chlorite, etc., are sharply curved and bent over the angles 
of the crystals lying in their way. It is clear, therefore, that much 
of the epidote here was in existence before foliation took place, 
though there is some of it of which it would not be possible to decide 
