- 10 -
gap in the ridge, and is now taking out the soft material to
make an almost circular pool behind the gap. At a point
opposite the gap, the pool has reached the chalk of Bindon
Hill, and this will slow down the erosion in the landward
direction, so that the pool will become more elliptical as
the gap gradually widens.
An earlier stage of the development of a cove like
Lulworth, is adjacent Stair Hole, where the gap in the
steeply dipping Portland and Purbeck beds is only a few yards
across, and the waves swirl through mysterious black caverns.
The softer rocks behind, are being washed out through this
honeycomb, but as yet the pool is small. A striking feature
of Stair Hole is the fantastically contorted strata of the
east face. Here one can sense the enormous forces in earth
movements that have squeezed these once-level layers of
sediments so that they are folded like layers of pastry. In
places they are vertical, then doubled over, cracked and
faulted, and their debris litters the floor of this basin.
Almost the final stages in the life history of a cove
can be seen further west at Durdle Door, where the gap in
the harder rocks has been widened out to make an open bay
and the softer rocks have been eroded right through to the
chalk. Some members clambered round to see the giant arch
that forms the 'door'. When this has eroded away, all trace
of the cove-like origin will have been lost, and by that
time Stair Hole and Lulworth Cove will have joined up as one,
leaving isolated jagged rocks offshore like the present-day
Mupe Rocks farther east.
For some of the party, hoping for a wealth of fossils,
there may have been a little disappointment in this stretch
of the coast, but I, for one, found this demonstration of
cove development one of the most interesting things we have
seen on these geological meetings.