|
Geology of Edderton Parish |
|
|
|
The bedrock of Edderton is composed of sandstones and conglomerates (pebble and boulder beds) belonging to the Old Red Sandstone formation. These rocks are of Devonian age, formed around 400 million years ago in a large inland lake that extended from Easter Ross northwards to Orkney and eastwards across the area now occupied by the Moray Firth.
These sandstones and conglomerates were derived from the wearing down
of mountains to the west which were created by the collision of the
continents of North America and Scandinavia during the Caledonian
mountain-building movements. Within the sandstone beds, which are
typically reddishcoloured but are sometimes grey or creamcoloured,
there are occasional beds of grey siltstone , a finer-grained
sedimentary rock. One of these beds, which outcrops in the
Muigh-bhlaridh burn at Blackpark, contains fossil fish remains (see
right) and is well known to geologists, being first described by the
famous early geologist, Hugh Miller of Cromarty. The sandstones can be
seen along the roadside cliffs between Edderton and the Dornoch Bridge
roundabout, where they have been quarried in the past and have provided
the sandstone slabs used by the Picts for the Edderton symbol stones.
In more recent times, quarries in this sandstone have provided the
stone for many of the older houses of Edderton and Tain. By walking up
the track from Leachonich to the top of Struie hill one can see a
change from red sandstones near the bottom of the hill to a rock
consisting of large angular blocks of older rock towards the top. This
latter rock is a solidified scree deposit formed on the slopes of
400-million-year-old mountains bordering the Old Red Sandstone lake.
There is no evidence within the Parish of the vast time period that
elapsed from the laying down of the Old Red Sandstone until, fairly
recently in geological terms, the impact of the last Ice Age. The
latter stages of the Ice Age were marked by glaciers that descended all
the major Highland valleys towards the Atlantic in the west and the
North Sea in the east. As these glaciers melted and retreated, vast
deposits of clay, sand and gravel, derived from the wearing down of the
glaciated terrain and carried
along by the glaciers, were formed along the margins and at the ends of the glaciers.
This material is collectively known as moraine , and forms long ridges ( lateral moraines ) and hummocks within the valleys.
Most of the bedrock in upper Edderton is covered by boulder clay left
by the glacier that moved down towards the Dornoch Firth from the
higher ground west of the Struie road. This clay is distinctive in
containing numerous pieces of rock ranging from small pebbles to large
boulders; the latter are known as " glacial erratics " and can only
have been transported by ice since they are composed of rocks only
found far to the west of their current position. Some of these are very
large and have been used from time immemorial by farmers for
constructing walls and buildings.
At the end of the Ice Age, around 9,000 years ago, the land surface
gradually rose after the weight of the ice had been removed, and a
series of raised beaches were formed around the coast of Scotland. Two
of these raised beaches can be easily seen in Edderton; the younger one
at about 5 metres above the current sea level forms large areas of flat
ground, for example at Meikle Ferry and Ardmore. The sea cliff fringing
this old beach follows the road between Edderton and Redburn.
The older, and higher, raised beach is at around 8 metres above current
mean sea level and forms the rather more undulating arable land at
Dounie and Edderton, including the Carrieblair battlefield. There is
evidence in the form of stone tools and shell middens that our
Stone-age ancestors inhabited the area at the time when this older
raised beach was formed, about 6,000 years ago. These raised beaches
contain a large proportion of sand and gravel and provide much better
farm land than the boulder clay of upper Edderton.
|
