W. M. Hutchings—Altered Igneous Rocks, Tintagel. 58 
little way off. Numerous large irregular grains of hornblende are 
seen set in a greenish-grey speckled mass. It is doubtless an ex- 
ample of the “ large-grained greenstone ” alluded to by De la Beche. 
A little way down the cliff the rock becomes much foliated, is 
much altered in general appearance, and is softer; and still further 
down, near the water, it has become very highly schistose, tolerably 
soft and easily fissile, differing in appearance in every way from the 
rock at the outcrop. Foliation is coincident with the dip and with 
the cleavage of the slates, shales, etc., above and below. 
Specimens were taken at three points: No. 1, outerop; No. 2, a 
few yards down the cliff; No. 8, near the bottom, a few yards above 
the level of the sea. Microscopic examination of sections from these 
specimens shows internal changes corresponding to the outward 
differences in texture and general appearance. 
No. 1 is essentially a hornblende-plagioclase rock. The horn- 
blende is all green, secondary and uralitic. It is mostly pale in 
colour with very moderate pleochroism, but some portions are of a 
much deeper colour and powerful pleochroism, the contrast being 
often seen in contiguous parts of one individual, one portion being 
nearly colourless, and the other a very deep green, though they ex- 
tinguish together and give nearly the same colours of polarization. 
The felspar is nearly all very turbid, but the columnar form of 
many of the crystals is still perfect, and they are still fresh enough 
to show twinning, binary and multiple. The structure of the 
original rock is shown to have been markedly ophitic by the fact 
that many of the individuals of hornblende are penetrated by felspar 
crystals, in some cases being nearly bisected. Crystals of apatite 
are seen here and there. There is comparatively little chlorite or 
calcite, but epidote is abundant, both in finely granular form in the 
hornblende and in crystals and irregular fragments and grains all 
over the sections. It is all quite colourless and non-dichroic. 
Leucoxene is plentiful in large plates and patches surrounding 
varying amounts of residual ilmenite; and some granular sphene 
may be seen. There are grains and little patches of secondary 
quartz, and a very few bits of perfectly water-clear, obviously 
secondary felspar, without any trace of definite form or of twinning, 
recognized by its optic behaviour. 
This rock is a typical epidiorite, of which we may say with 
tolerable certainty that it was derived from a coarse-grained ophitic 
dolerite. 
Sections of No. 2 show that hornblende is much diminished in 
quantity, with a corresponding increase in chlorite. All stages may 
be seen of the passage of the hornblende into chlorite. Calcite is, 
also very much increased in amount. 
The felspar is largely in the state of a confused, crushed, turbid 
mass mixed up with chlorite, without any form or sign of twinning, 
but with this there are a very large number of bigger grains and 
patches which are water-clear and contain needles of hornblende in 
some cases, together with numerous grains of chlorite. But few of 
these water-clear bits show any twinning. Quartz has increased 
