W. MM. Hutchings—Altered Igneous eee Tintagel. 103 
Where this coarse lamination is most developed it would almost 
lead one to believe that it represented an original stratification, or 
bedding, of different materials; but this impression is much weakened 
by the fact that this coarsest structure can be traced, in a short 
distance, passing gradually into finer and finer foliation, and finally 
into rock in which the chloritic and stony materials are so closely 
interwoven, so to speak, as to be no longer separable by eye or lens. 
The material of the hard layers is of a slightly bluish-grey colour. 
It sometimes contains numerous crystals of magnetite, but beyond 
this and occasional grains of calcite no separate minerals can be 
made out with a lens. It effervesces so briskly with acid that this, 
and its appearance, might easily cause it to be set down as calcite, 
but its hardness and the fact that fragments do not dissolve, nor 
even disintegrate, in acid, show that its main component is not calcitic. 
Portions of contiguous, very coarse, hard and soft layers were sub- 
mitted to microscopic examination, and a description of them is in- 
teresting, not simply as bearing on this special form of occurrence, 
but also because, with slight modifications, a more or less intimate 
mixture of these two materials makes up a great part of the entire 
sheet of rock. . 
The material of the hard layers may be best described by saying 
that grains of calcite, and grains and more or less imperfect crystals 
of felspar, are set in what may for convenience be called a sort of 
“‘ sround-mass ” of felspar, chlorite, small grains of calcite, muscovite 
flakes, and quartz, with much iron ore. 
The larger bits of felspar are mostly of quite indefinite and 
rounded outlines, though a few of them show a certain amount of 
regular shapes. Some of them show well-developed cleavage, but 
twinning is so rare as to be practically absent. All are quite water- 
clear, but are more or less full of minute flakes of muscovite. 
In the “ground-mass” felspar very much predominates. Its 
degree of intermixture with the other materials varies, so that at 
some parts of a slide the whole forms a very fine-grained mosaic, 
while at others it is much more coarsely compounded. Grains of 
felspar of ample size to permit of optic tests for its discrimination 
from quartz are plentifully dispersed throughout. It is all brilliantly 
water-clear, and no sign is anywhere seen of any definite forms, nor 
of any twinning. The quartz is wholly secondary, and is rather 
irregularly dispersed, as single larger grains and as a fine-grained 
mosaic, either alone or in intermixture with felspar and chlorite. 
Flakes of muscovite abound throughout the entire mass. Sphene is 
very plentiful in transparent colourless grains and as rather larger, 
brownish, less transparent bits; and a good deal of leucoxene is 
seen in various stages of progress to granular aggregates of sphene. 
A little rutile is present, mainly in the larger bits of chlorite. 
Iron ores are diffused in very great abundance all over the 
sections. Crystals of magnetite predominate, but there is a great 
deal of rounded, crushed and quite indefinite form down to almost 
a powdery condition. Among this, small, ragged, flat, thin, plates 
may be seen, and some thicker tabular bits, but there is nothing 
