Regional Geology, Midland Valley
The Midland Valley of Scotland, lies between the Highland Boundary Fault
and the Southern Upland Fault.
Some of the oldest rocks in the Midland Valley region date from the Ordovician
period, around 470 million years ago. At that time northern Scotland lay
at the southern edge of a continent known by geologists as Laurentia with
the area that was to become the Midland Valley, forming a line of island
volcanoes in the adjoining and gradually closing Iapetus Ocean. The Iapetus
Ocean closed during Silurian times, in a continental collision known as the
Caledonian Orogeny. This joined the crustal foundations of both Scotland
and England.
Erosion of the mountains to the north and south, produced sand, silt and
mud that was carried in to the Midland Valley area, covering the remains
of the volcanic island chain. By Devonian and early Carboniferous times,
Scotland lay just south of the equator. The climate was hot and dry, with
seasonal rains. Rivers laid down 'The Old Red Sandstone' and volcanic activity
gave rise to extensive lava fields.
Ballagan Glen north of Glasgow an excellent section through
Lower Carboniferous sedimentary rocks known as the 'cementstones'
During the Carboniferous, around 320 million years ago, Scotland lay on
the equator with a tropical climate. Corals grew on reefs in warm shallow
seas and swampy forests that flourished in a 'Greenhouse' atmosphere, gave
rise to coal. Volcanoes such as Arthur's Seat in Edinburgh dotted the landscape.
Kings Cave raised Shoreline and sea cliffs fashioned from Permian
sandstone on the Isle of Arran.
Image provided Scottish Natural Heritage
When Scotland lay in the desert belt north of the equator, during Permian-Triassic
times around 250 million years ago, sand dunes and flash flood deposits were
laid down. These can be seen in Ayrshire and Arran.
The remains of a 60 million year old volcanic complex on Arran, represents
a time when there was intense volcanic activity along the western margin
of Scotland. This occurred when north-west Europe was being split from
North America, with the formation of the North Atlantic
This area contains
a wide variety of lowland glacial landforms and deposits, coastal landforms
and deposits and active river landforms.
The effects of glacial erosion in this area are more subtle than in the
Highlands. Pre-existing valleys were over-deepened but later infilled with
drift, and the hills moulded and streamlined by the passage of the ice.
Striking examples of such moulding are represented in the crag and tail
forms and streamlined bedrock of Midlothian and East Lothian. The northern
mountains of Arran display many classic landforms of mountain glacial erosion.
The lower ground is mostly covered by a cover of drift deposits, comprising
of till and sand and gravel, from the last and earlier ice sheets. These
deposits have a range of surface forms, including, eskers, kames and outwash
terraces. Notable examples include the drumlin field of the Glasgow area
and the nationally important Carstairs Kames.
Glacial till and fluvioglacial deposits in a river section
near Muirkirk Ayrshire.
Image provided by Scottish Natural Heritage.
The Loch Lomond area provides evidence for the final episode of glaciation
at the end of the ice age. This is known as the Loch Lomond Readvance,
a glacial event which occurred between about 12,600 and 11,500 years ago.
A distinctive aspect of the coastal scenery in the west is the pronounced
shore platform and its associated cliff line, part of the Main Rock Platform.
The western Forth Valley has one of the most important records of relative
sea-level change in Scotland. Here a sequence of buried beaches and carse
deposits provide a record of changes during the last 12,000 years. The
coastal lowlands of Angus Fife and East Lothian, provide widespread evidence
of sea level changes, in the form of raised shorelines and the extensive
development of carselands.
Geological
map of Midland Valley region
