104 W. iM. Hutchings—Altered Igneous Rocks, Tintagel. 
which could safely be set down as ilmenite, unless it be a few ex- 
tremely thin flakes, faintly translucent, with brown colour, in some 
of which sagenitic rutile is visible. ‘These appear to be micaceous 
ilmenite. It may be as well to remark here that throughout all the 
sections examined from this sheet of rock, magnetite is the only iron 
ore which can be specified with certainty. Crystals of it are very 
abundant, and it is seen that though the greater part of it was 
formed prior to, or during, the foliation of the rock, much has also 
been formed since. Much, if not nearly all, of the rounded, flat- 
tened and totally crushed material is also magnetite; the deforma- 
tion of crystals under pressure and movement is seen in various 
stages. Larger plates, with or without leucoxene, which could be 
classified as ilmenite, are not seen anywhere. Tabular fragments of 
fair size occur often enough, and leucoxene is present frequently 
with them; but this, as Mr. Teall points out (British Petrography, 
p: 167), is not enough to warrant their being set down as ilmenite, 
because the same result might be equally obtained from titaniferous 
magnetite in decomposition. The presence in the rock of a notice- 
able amount of leucoxene, together with the abundance of sphene 
and rutile, make it probable that ilmenite was originally present in 
considerable quantity, but is now represented mainly by alteration- 
products. As bearing on the nature of the original material of this 
sheet the question as to ilmenite is, of course, of considerable im- 
portance, and I have looked carefully for any cases of its definite 
occurrence. 
The corresponding soft layer does not really differ essentially in 
nature from the hard layer. The chlorite has increased much in 
quantity and is in larger pieces. Muscovite also is present in larger 
amount and in larger flakes and crystals, and also in good-sized 
patches. Calcite is less in quantity, while quartz again is much 
increased. Jor the rest, there is the same ground-mass of felspar, 
chlorite, ete., only that it is not so regularly diffused. There are 
plenty of large grains of water-clear felspar, and several bits show 
more or less of twinning. There is a prevalence of very intensely 
undulous extinctions in the felspars and quartz grains, due to great 
mechanical stresses. This is more marked here than in any other 
part of the sheet. The same is true of the minerals of the hard layer, 
but not in quite so great a degree. The iron ores are very much 
more in a crushed condition here too. A high power shows the 
diffusion of minute grains and crystals of rutile all through the 
sections, together with other grains and microlites which are 
indeterminable. 
Microscopic study of these layers, therefore, does not bear out the 
idea that they are connected with any original bedding of materials 
of different nature. Much as they now differ in physical condition 
and general appearance, their constitution is mineralogically the 
same, and, it is an interesting question as to how this local separation 
into bands has taken place, and how it is that while the soft layers 
are highly foliated and split easily into thin pieces, the hard layers 
have not a trace of such foliation or cleavage. 
