|
The geological and geomorphological
features of Portland played an important role in the settlement of the
island and in the subsequent lifestyle of the prehistoric populations.
|
Portland is referred to as
an island but is really more like a peninsula, connected to the
mainland by the Chesil Beach. The archaeologcal site of Culverwell
is situated near the present southern tip of the 'island', about
halfway on the slope of a south-facing hill and is about 270m
east of a stream by that name.
Explore all graphics with mouse
for locations
|
 |
Sea-levels:
People first came to Portland during one of the last phases of the last
glacial epoch between about 12,000 to 10,000 years ago (see Time
Line). During the cold phases, when a lot of water was contained
within the glaciers in the northern parts of Europe the sea -levels
and river-levels were lower than today. England was at times connected
to Europe and animals and people would have been able to walk dry-shod
into the area which is now Portland.
The edge of the sea at high levels
would, of course, have been much further out than today from the Bill.
At the time the Island was occupied by Mesolithic people, e.g. at Culverwell,
the edge of the sea would have been approximately 300m further out than
today and there would have been a gradually sloping beach between the
cliffs and the water.
During the warmer phases, the
sea-levels rose. It was during such phases of high sea-levels 120,000
or more years ago that the Raised Beaches at Portland Bill were
formed. There is evidence of two Raised Beaches in the Bill area
at heights of 18-14m and 11-7m (approximately 60 and 30 ft) above
the present sea-level. Both consist of a thick deposit of sea pebbles
and molluscs on top of the limestone beds of the Jurassic period.
These beaches are capped by deposit of yellow loam and limestone
rubble, sometimes referred to as the 'Head'.
|
 |
This rubble is of importance as stones
and slabs from it was much later used by the Mesolithic and later prehistoric
people to build their homes and make their tools and therefore played
a vital role in the early settlement of the Isle.
|
Chesil Beach and Fleet:
The Chesil Beach
is a fairly unique feature
which, without doubt,
played a very important
role in the economy and lifestyle of the earliest settlers of
Portland. It is an immense off-shore bank of beach pebbles which
stretch from the north-western cliffs of Portland near a place
known as Smallmouth and joins the mainland (at present) in Lyme
Bay. This Beach was formed during one or other of the glacial
epochs by wave action from an older beach further out to sea.
Near the Portland end of the Beach the pebbles are mainly Portland
chert but further away the ratio of other pebbles, such as flint
and quartzite, increases.
Between the Beach and the mainland is a seawater lagoon known
as the Fleet. During the early Mesolithic period this lagoon would
have been much larger than today and contained freshwater, fed
by streams from the hinterland; when the sea-levels gradualy rose
to their present height, the sea created a breach in the land
and flooded in.
Large numbers of Mesolithic artefacts made of Portland chert occur
all along the landward shore of the Fleet, diminishing only slightly
in numbers from Abbotsbury westwards. This demonstrates beyond
argument that anciently people from Portland had frequented the
Fleet, probably to collect various food products and probably
also to meet with other groups of people for the purpose of trade
and community contact (see economy).
|
Caves:
Numerous caves round the coast of the Island, particularly in the
Bill area, were formed by the action of the waves as the sea-levels
rose and fell. Although no archaeological remains have been found
in them (with the possible exception of perhaps one), the caves
were almost certainly frequently used by the ancient island dwellers.
They would have camped or .picknicked' in them whenever they were
on the shore to collect molluscs or pebbles or bigger lumps of stone
for tool-making. Although the evidence for fishing was very scarce
on the Culverwell site, fish may have been regularly caught and
possibly consumed on the beach. Sea-weed is another product the
prehistoric folk may have used. |
 |
Jurassic Chert:
The Isle of Portland consists of Jurassic marine Portland Beds (average
44m thick) with a covering of freshwater Lower Purbeck Beds (average
7m thick). Within these Beds are seams of siliceous dark cherts.
All along the coast of Portland very distinctive thick seams of
black or dark grey Portland chert are visible. When hit with a hammerstone
this chert fractures easily and neatly in such a way that flakes
or blades come away and can be formed into tools (see Artefacts). |
 |
Climate:
During the Mesolithic occupation of Portland, at about 8,000 years ago,
the temperature would have been a degree or two higher than today. There
would have been some more small shrubs and bushes on the island than
today and also many more streams.
|