466 J. H. COLLINS ON THE SERPENTINE AND 
of what appears to me to be a thin bed of interstratified serpentine. 
This lies between beds of the soft red decomposed shale just referred 
to, and after a few yards is succeeded by a much thicker bed. This 
second bed contains in its upper part thin bands of the hornblende 
schist, some of them exhibiting a perfect passage from one rock to 
the other. Succeeding this bed of serpentine, which is perhaps 
40 feet thick, is a very thick mass of hornblende schist. All the beds 
at first dip sharply to the south of east, and afterwards they exhibit 
the great flexures shown in the sections, in addition to many minor 
curves. The whole series appears to me to be interbedded, each 
rock following closely the flexures of the other. The succession of 
the beds is best seen at and below high-water mark, as the cliffs 
hereabout are extremely ruinous, being traversed by numerous joints 
and minor faults. The joints are frequently lined with minute 
crystals of ilmenite or with crusts of calcite, and the little fissures 
are frequently filled with asbestos, calcite, or aragonite. Chemical 
action is still going on here to a considerable extent. 
The great bed of serpentine is for the most part dark greyish- 
green, a few only of the bands heing red. Many have a rich oil- 
green tint, others a granulated appearance, reticulated with thin 
bands of dark green. 
Hornblende Schist.—The hornblende schist of Porthalla is a very 
peculiar rock indeed. It is very little fissile, the schistose structure 
being limited to a series of alternations of dark and light bands of 
its constituent minerals. These are as follows: 
(a) A dark green hornblendic substance of very indistinctly erys- 
talline appearance, and which differs optically in a very marked 
degree from the ordinary hornblende of the Lizard rocks, especially 
in the absence of dichroism and of cleavage. 
(6) A pale grey or cream-coloured uncleavable “ felspar ” of the 
kind known as saussurite, which has very little effect on polarized 
light, and which also exists in very undefined forms. In both 
these minerals there is a remarkable vagueness of outline, such as we 
might expect would result if the whole mass had been in a state of 
semi-fusion. The heat resulting from enormous local pressure such 
as these rocks have certainly been subjected to, would quite account 
for this indistinctness of outline in the constituent minerals. 
The rock of course varies in composition as a whole according to 
the predominance of the dark green “ hornblende” or the creamy 
white “ felspar ;” analyses showing the composition of the rock as a 
whole, and of each constituent separately, are given later on (p. 468). 
At a distance of about a third of a mile from the Cove, the large 
quarry in massive hornblende schist known as Hickes’s can be 
reached along the shore at low water. Beds of serpentine alternating 
with the hornblende schist can be traced nearly up to this point, and 
partaking of all the plications and contortions of this latter rock. On 
reaching the quarry, however, the strata seem to be nearly vertical ; 
the serpentine plunges suddenly downward, and is seen no more for 
a considerable distance. 
From here to Dranna Point the coast section can only be 
