The Geology of Luffness and the Surrounding Area
Let us consider a simplistic model of the
landscape. In this model there are three layers one on top of the
other. People have used the lower two levels for many reasons, but it
is the upper most layer that man has had the greatest influence on.
This surface layer contains a visible record of man's occupation.
Here we may find traces of passed civilisation, from the ghost of an
ancient village revealing itself as a crop mark, to the solid
concrete of a disused airfield. Here on the surface we live among our built environment, streets, field systems, golf courses, woods
and all the nameless bits between them all. However, it is never
quite this simple because what was on the surface one thousand years
ago may now be buried in the next layer down.
The next layer down is what geologists may call
the 'superficial deposits' or 'overburden'. This layer contains the
soil on which life at the upper surface depends. Most soili
consists of a mixture of disintegrated rock and some organic remains.
The mineral content of the soil usually comes from the process of
weathering and erosion in which the elements wear down the exposed
bedrock.
The bed rock is the third and lowest layer in our
model. This strata formed first, and often determines the nature of
the overlying two layers.
The bedrock of the Luffness area
Now let us look at how and when the earliest rocks
in the Luffness area were formed. We need to go back to a time before
man, back to a time even before the dinosaurs, in fact we have to go
back to 350 million years ago to the Carboniferous period. At this
time the land that would become Scotland was situated over the
equatorii.
The area was dominated by tropical forests;
whose buried remains would go onto form the Scottish coal fields. The
land that would form East Lothian was a flat coastal plain, clothed
by forests, dotted with lagoons and crossed by meandering rivers
flowing into deltas at the edge of a sea to the north eastiii.
This landscape was punctuated by volcanic
activity. Magma was forced up through the crust to erupt onto the
surface. Once on the surface the magma formed lava flows and
gradually formed a cone around the volcanic crater. This was the time
when the volcanoes that would produce The Bass Rock and North Berwick
Law were active.
If
we look at a map of the underlying bedrock (illustration
1)iv
we can see that about one third of the area is made up of a volcanic
rock called Trachytev,
which is thought to have been formed by the crystallization and
abstraction of iron, magnesium, and calcium minerals from a parent
basaltic lava. Basaltvi
is the Earth's most abundant bedrock. It was formed when the lava
cools quickly on the surface to form a rock of a fine grained
texture. If the molten magma was trapped within the Earth's crust it
cooled slowly to form a coarse grained rock of of variable
composition called Gabbrovii.
One
feature formed by magma that never made it to the surface is a sill.
A sill forms when the magma is forced sideways through the layers of
strata, forcing them apart and then solidifying. An example of a sill
can be seen (illustration
2)
at Gullane Pointviii.
.jpg) |
| Illustration 2: British Geological Survey. © NERC. All rights reserved. Image digitised with Grant-in-Aid from SCRAN (Scottish Cultural Resources Access Network) |
The British Geological Survey describes it thus:
'The dolerite sill, technically a teschenite, is intruded into the Carboniferous Calciferous Sandstone Measures. As this igneous rock is much harder than the overlying and underlying sedimentary rocks it has withstood erosion better and so now forms a headland.''ix.
The non volcanic rocks of the area are principally
the sedimentary rocks; sandstone, mudstone and siltstone. These rocks
differ in the size of grains they are formed from. Limestone is
another sedimentary rock that forms Aberlady Point. Limestone was
formed from the remains of coral reefs and marine sediments produced
by the tropical seas of the Carboniferous periodx.
Now
that we have looked at the underlying bedrock we will move up the
strata to the next layer; the superficial deposits (illustration
3)xi.
To understand how they formed we need to realise that during much of
the past two million years, East Lothian was buried under an ice
sheet many hundreds of metres thickxii.
As the enormous weight of this ice bore down on the crust it caused
the underlying more viscose mantle material to flow outwards away
from the force, which in turn allowed the crust to sink. The ice
sheet was not static but flowed west to east across the county. As it
did it picked up boulders and fine rock dust which slowly eroded the
underlying features. This ice flow carved valleys in an east west
orientation and revealed rock formations from the lower layers. The
glaciers scoured the volcanoes grinding their cones down to the more
resistant rock. It is this resistant rock that forms the remaining
plugs that we see today. As well as being an eroding process the ice
sheet deposited large amounts of material to form a new uncolonised
landscape. These deposits of silt sand and clay have developed over
millennia into some of the richest farmland in Britain.
The ice melted for the last
time in East Lothian about 14 000 to 16 000xiii
years ago and the sea level rose. With the sea came beaches,
but the sea volume dropped and the land was elevated due to post
glacial rebound. This is the return flow of the mantle material once
the deforming weight of the ice has been removed. Very slowly the
crust rises over thousands of years until it reaches an equilibrium
level. This level is has not been reached yet but the rate may be
less than quoted for Dunbar at a rate of 55mm a yearxiv,
which sounds rather extraordinary. Whatever the rate, this still left
the beaches stranded from the sea that formed them. This gives us the
feature known as a raised beach. A raised beach can be seen on the
flank of Gala Law at about eight metres above the present sea level,
in what now forms part of Luffness Links.
The predominant overlying geology of this area are
the wind blown sands. Along the coast the sands and silts of the
beaches are light enough to be readily carried along in the wind,
particularly where exposed and dry in the intertidal zone.
Onshore movement of sand has produced sand dunes, which became
stabilized by plants. Characteristic vegetation communities developed
on the sand dunes and dune slacks but, as the shoreline has continued
to move towards the sea, the older inland plant communities have
developed from sand dependent and salt-tolerant communities into more
uniform grassland communitiesxv.
The raised beach terraces are home to the naturally occurring fine
grass species such as Festuca rubra and it is these grasses
which make this coast so suitable for the establishment of many fine
golf courses.
Having said that, it would be many years before
any golf courses were formed. The land as we leave it after the ice
melted was uninhabited and would pass through many years before the
first people colonised it. It is the evidence of these first people
that we examine in the next chapter.
References
iAberlady
Bay Local Nature Reserve, Descriptive Management Plan, East
Lothian District Council, 1977.
The full details of the soil
survey are included in the plan in Section 6, on page 15 and in
drawing 4. I have included these in Appendix A.
iiEast
Lothian and the Borders:A Landscape Fashioned by Geology.
1997. Scottish Natural Heritage: page 17.
iiiEast
Lothian and the Borders:A Landscape Fashioned by Geology.
1997. Scottish Natural Heritage: page 4.
ivMap
product: British Geological Survey 1:50000. Map printed at 1:25000.
Digimap.edina.ac.uk/geologyroam/mapper
viiiEast
Lothian and the Borders:A Landscape Fashioned by Geology.
1997. Scottish Natural Heritage: page 7.
ixDigimap.edina.ac.uk/geologyroam/mapper
xEast
Lothian and the Borders:A Landscape Fashioned by Geology.
1997. Scottish Natural Heritage: page 17.
xiMap
product: British Geological Survey 1:50000. Map printed at 1:25000.
Digimap.edina.ac.uk/geologyroam/mapper
xiiEast
Lothian and the Borders:A Landscape Fashioned by Geology.
1997. Scottish Natural Heritage: page 18.
xiii
Lambeck K, 1995: Late Devensian and Holocene shorelines of the
British Isles and North Sea from models of glacio-hydro-isostatic
rebound,Journal of the Geological Society-London, Vol. 152, 1995,
pp. 437–448
xivMoffat
A., 2005, Before Scotland: The story of Scotland Before History,
ISBN. 0500005133X, Page. 30.
xvRoger
P. Kirby (1997): The Aberlady Bay coastal landforms and vegetation
communities, Scottish
Geographical Magazine, 113:2,
121-126
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