102 W. WW. Hutchings—Altered Igneous Rocks, Tintagel. 
structure and composition, all appear to affirm it. In the Trebarwith 
cliffs it is again dipping steeply towards the sea. The upper few 
_yards of it only are seen, the deeper portions underlying the beach. 
For a great part of the distance, and indeed wherever the rocks have 
not been disturbed by falls of cliff and landslips, the contact with 
the overlying sedimentary rocks is very sharply defined. 
At the south end of the Strand the sheet disappears under the 
sedimentary rocks of Dennys Point, and so far as I am aware, it does 
not show again in the cliffs going southwards; certainly not for 
some three miles or so examined by me wherever accessible. 
Whether or not it has any connection with the igneous rocks near 
Port Isaac I do not know. 
Near the south end of the Strand a valley, with a road, comes 
down to the shore. A little way up this road good sections of the 
entire thickness of the sheet are obtained, near the little village of 
Trenow and on the opposite side of the valley. It here again forms 
escarpments in which its upper and lower contacts with shales are 
sharply defined, and is again cut off abruptly as at Bossiney. 
We can thus trace this sheet of rock, from north to south, for 34 
miles. Its thickness may, on a rough average, vary from 70 to 100 
feet. It doubtless originally continued some distance inland. De 
la Beche speaks of some parts of it (the northern) as connected with 
rocks several miles away, so that it evidently formed part of a very 
considerable igneous mass, which was older than any of the rocks 
already noticed. 
Considered petrologically this occurrence is very interesting. 
Macroscopically, the chief observable components are green chloritic 
minerals and calcite. At some points micas more or less replace the 
chlorite. Pyrites and magnetite are seen in varying amounts, and at 
some parts epidote crystals in plenty may be noticed with the naked 
eye. Foliation is highly developed throughout, always coinciding with 
the cleavage of the slates and shales above and below. ‘The texture 
of this foliation varies in every degree, from a fissility almost equal to 
that of a slate to a series of bands or layers of considerable thickness. 
Both texture and mineralogical composition vary so much at 
different points that it would be equally useless either to attempt to 
give one description that should apply to the whole of the sheet, or 
to give detailed accounts of all of the series of sections I have ex- 
amined from different parts. A better general idea will be conveyed 
by picking out and describing a few of the most strikingly charac- 
teristic examples. 
At several places the rock is seen to be very coarsely laminated, 
layers of comparatively soft chloritic or micaceous material alter- 
nating with others of a hard, compact, non-foliated stony substance. 
This is seen most strongly exemplified towards the south part of 
Trebarwith Strand, where the layers of the stony material are as 
much as 14 to 2 inches thick in some cases, the softer layers being 
rather less. A serrated form results from weathering at these parts 
of the cliffs, the soft layers wasting away and leaving the hard ones 
projecting. 
