58 W. M. Hutchings—Altered Igneous Rocks, Tintagel. 
hornblende. The felspar is much the predominant constituent, and 
part of it is better preserved here than in any other local rock I have 
examined. Much of it is again in the indefinite and untwinned 
water-clear condition, but with this there are a great many well- 
twinned crystals of columnar form. Binary twinning is most 
prevalent. A series of measurements of maximum extinctions 
shows that much of the felspar belongs to the labradorite-anorthite 
group, though more acid felspars seem to be present, most likely of 
secondary metamorphic origin. Chlorite and calcite are in only 
moderate amount. Secondary quartz is tolerably plentiful, both in 
grains of good size and as a mosaic of smaller ones. Leucoxene 
with residual ilmenite, granular sphene, a little epidote, apatite, small 
flakes of biotite, and rutile in slender needles, and bunches of 
needles go to make up this rock. Bent and broken crystals of 
felspar, and strongly undulous extinctions both of felspar and quartz, 
bear witness to severe strain. The fact that much of the quartz 
shows these effects of stress goes to prove that_the rock was very 
much altered before this stress was applied. 
In the centre of the Cove, almost under the waterfall, another 
exposure of igneous rock is seen, quite at the bottom of the cliff. 
The extent of it visible is small. It makes the impression of being 
the upper part of a curve or fold of a sheet. If this is so, and 
supposing the sheets to be contemporaneous and not intrusive, this 
rock is older than the last described, considerable thickness of 
sedimentary material intervening. This rock is very schistose. it 
is highly altered, very little of its abundant felspar having any 
definite formas compared with the last. Calcite, chlorite and quartz 
are in large amount, there is also much ilmenite in various stages 
of alteration to leucoxene, and many of the large patches of 
chlorite are full of beautiful sagenitic rutile. 
Again, passing from the Castle Cove hy the path between the 
mainland and the so-called “island” of Tintagel Head, and de- 
scending to the shore below the steep west cliff of the mainland 
part of the Castle, we come upon a section of several sheets, or. 
bands, of igneous rocks of various thickness, with intervening black 
shale. The upper sheet is some feet in thickness, then comes a bed 
of shale in which are two or three sharply separated bands of 
igneous rock of a few inches only, and finally a lower sheet of 
which some four to six feet are seen. hey are only exposed for a 
few yards. It is not possible to make out anything with certainty, 
but very probably the upper portion of this exposure is connected 
with the rock seen near the waterfall in the Castle Cove. 
I have examined specimens from the upper band of the series. 
It is again a very schistose rock. Microscopically it is interesting 
because it contains a good deal of what may undoubtedly be con- 
sidered to be original igneous structure. The felspar, very abundant, 
is partly turbid and partly water-clear, and all the larger individuals 
are more or less full of flakes of muscovite. Crystal forms are well 
retained, and twinning, both binary and multiple, is very little 
obliterated. Tabular crystals are most numerous, but columnar 
