The walk will be short, but does involve crossing the Finny River using stepping
stones.
Knockkilbride and the Finny River area are renowned as the site of an ancient volcano
(490 million years old), formed as the lapetus ocean closed to bring the two halves
of Ireland together. The actual landform of the volcano is long gone but some of
its rocks are preserved. Eruptions at the "Finny Volcano" were of two types:
runny basalt magma formed pillow lavas, stacks of interlocking lava balls, when
blobs of lava were chilled by eruption into water: sticky andesite magma broke up
to form breccia deposits of rock fragments. Quiet periods between eruptions allowed
very fine sediment to settle and form red and green chert.
Park in the lay-by on the narrow road at Cummer, between Finny and Maumtrasna pass,
from where a beautiful view takes in Lough Nafooey. Walk downhill along the road.
At the first bend to the right not the stream gully, which marks the trace of a
major fault in the rocks that truncates the volcanic rocks and juxtaposes them against
with the Finny road.
The low cliff on the left is made of pillow lava. The most obvious rounded shapes
of whole pillows (up to 50cm across) are on the right end of the cilff. Look for
small holes in the rock: these were formed when gas bubbles
 in
the molten lava were trapped as it cooled and solidified. Note how they are concentrated
in rings concentric with the edge of pillows. Continue to the road junction and
cross onto the track. The first outcrop on the left is of angular fragments (not
rounded like the pillows) of the "sticky lava" held together by fine sediment. The
large fragmens (up to 30cm across) are obvious, but look closely and the edges of
many smaller ones can also be distinguished. This outcrop also has a streak of red
cherty sediment running trough it.
When the Finny River is low, it can be crossed using the stepping stones at the
end of the track. Several outcrops on the other side show further examples of the
fragmentary "sticky lava" and layered red and green cherts. For the adventurous,
the very best pillow lavas occus at the top of Bencorragh, where exposure to weathering
has etched them (and from where there are beatiful views over Derry Bay and Lough
Kilbride). |