File:The Quarterly journal of the Geological Society of London (12645065163).jpg

10 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. .May 17,
(the beds still uninterruptedly dipping south,) at the Dally Bay,
graptolites again occur in a red flag or tilestone. Still further north,
the beds for about a mile have a reversed dip to the north, after
which they recover their southerly dip, then gradually become vertical,
and at the extreme north point of the peninsula they plunge into the
sea at a very high angle to the north. These vertical and highly
inclined beds near the Corswall Lighthouse are very remarkable from
their containing beds of conglomerate of a coarser nature than any I
have ever seen described as occurring in so old a formation, with the
exception of those of the Potsdam sandstone, described by Mr. Lyell
as old Silurian. The fragments generally vary from the size of one
inch to a foot in diameter ; but in some of the beds, boulders of three,
four, and even five feet diameter occur. They are well-rounded, and
principally consist of red quartziferous porphyry and a large-grained
grey syenite ; but serpentine, red jasper, and other rocks occur ; and I
have found one or two instances of large angular fragments of grey-
wacke. There are no rocks in the neighbourhood, as far as I know,
from whence any of these rounded fragments could have been derived :
serpentine, it is true, occurs in great quantity at the Bennan Head,
two miles and a half north of Ballantrae ; but it can be proved that
that serpentine is of a considerably newer date, since it has penetrated
and altered sandstones newer than the coal-measures. The matrix
of this conglomerate is sometimes a green, trappean-looking sand-
stone of exceeding toughness, and sometimes an indurated sandstone
indistinguishable from many common varieties of greywacke. The
beds are well-exposed for a great extent ; they are cut across in many
places at right angles to their strike by deep fissures, resembling
those in Arran and elsewhere occasioned by the decomposition of a
trap dyke. These fissures afford abundant e\adence that these con-
glomerates are vertical beds, in every respect conformable to the
flaggy greywacke which is found to the north, to the south, and
sometimes mterstratified with them. Their vertical position is in-
dependently shown by the smaller pebbles being arranged in per-
pendicular layers, and by the greater diameters of the larger boulders