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Geology of Aberdeen

 

Being sited between two river mouths, the city has little natural exposure of bedrock. This leaves local geologists in a slight quandary: despite the high concentration of geoscientists in the area (courtesy of the oil industry), there is only a vague understanding of what underlies the city. To the south side of the city, coastal cliffs expose high-grade metamorphic rocks of the Grampian Group; to the south-west and west are extensive granites intruded into similar high-grade schists; to the north the metamorphics are intruded by gabbroic complexes instead.  Under the city itself? The small amount of geophysics done, and occasional building-related exposures, combined with small exposures in the banks of the River Don, suggest that it's actually sited on an inlier (Older rock formation) of Devonian "Old Red" sandstones and silts. The outskirts of the city spread beyond the (inferred) limits of the outlier onto the surrounding metamorphic/ igneous complexes formed during the Dalradian period (approximately 480-600M years ago) with sporadic areas of igneous Diorite granites to be found, such as that at the Rubislaw Quarry which was used to build much of the Victorian parts of the City.

On the coast, Aberdeen has a long sand beach between the 2 rivers, the Dee and the Don, which turns into high sand dunes north of the Don stretching as far as Fraserburgh; to the south of the Dee are steep rocky cliff faces with only minor pebble and shingle beaches in deep inlets. A number of granite outcrops along the south coast have been quarried in the past, making for spectacular scenery and good rock-climbing.

The city is built on many hills, with the original beginnings of the city growing from Castle Hill, Heading Hill, Woolmanhill, Porthill, Mounthooly, St. Catherine's Hill and Windmill Hill.  Two earthquakes are recorded one occurred ion 9 September 1608 and the other on the 18th Augiust 1816 with no structural damage.

Sands of Forvie

The Sands of Forvie represent excellent examples of active geomorphological processes. Here, an outstanding beach-dune complex has developed over the last 4,000 years, forming one of the largest areas of blown sand in Scotland. The area has attracted researchers of coastal landforms and processes for many years.  The sands stretch for 24km north along the coast from Aberdeen. Three large rivers have their estuaries along this stretch (the Dee, the Don and the Ythan), and the Sands are split into 2 components: the Forvie peninsula and Foveran links, with the Ythan estuary marking the boundary between the two.  Present day processes include winds, waves and tides, with the dominant direction for sediment movement being northwards.  The sands formed largely as a result of deglaciation at the end of the last ice age.  Following the melting of the last Scottish glaciers approximately 10,000 years ago, vast quantities of sediment were transported by rivers to the coast where they were deposited off-shore. However, as sea levels rose due to the melting of the Scandinavian and North American ice sheets (peaking approximately 4,000 years ago), these sediments were reworked and deposited back onshore.  The northern part of the Forvie Peninsula exhibits classic parabolic dunes and sand hills.  The area is underlain by a till covered plateau.  The southern part of the peninsula has well developed dune complexes and dynamic sand hills.  Sand waves run in a North South direction, defining this sand peninsula. The area is underlain by glaciofluvial, raised estuarine and beach terraces.  A large, dynamic sand dune complex exists at Foveran Links.  Longitudinal bars are found at the southerly end, merging into a shifting sand bar and spit complex at the northern end (at the Ythan estuary).  This occurs due to the northerly drift of sediment.

Sand dunes at Forvie- an outstanding beach-dune complex has developed over the last 4,000 years, forming one of the largest areas of blown sand in Scotland.

The Forvie National Reserve lies on the Ythan Estuary just outside Newburgh, around 20 miles north of Aberdeen. The area is even dubbed the “Northern Sahara” due to all of the sand left after the last ice age around 15,000 years ago. The present dunes are thought to be around 2000 years old.  The mud flats in the estuary are home to many types of marine life and birds.  There was a village here in the past which disappeared under sand in the 15th century,  Local folklore lays this blame of this occurrence on Forvie’s Curse, where according to local folklore, 3 sisters were set adrift in a leaky boat so that they could not inherit.  The sisters placed a curse on Forvie, saying that it should only contain thistle and sand. The curse resulted in a fierce storm which covered the village in sand.

Aberdeen’s roots go back to prehistoric times when small bands of hunters moved northwards behind the retreating ice at the end of the last ice-age.  The original settlement, referred to as Aberdon, lay at the northern end of modern-day Aberdeen, the area now known as Old Aberdeen or Aulton, (or Old Town).  Marauding Danes sacked and burned the settlement in the 900s but the continued growth of Aberdeen was inevitable because of its importance as a port. The period from 1100 to the present day is detailed in the City Archives, one of the oldest and most complete civic records in Scotland.

North East Scotland Geology


Aberdeen: topographical, antiquarian, and historical papers on the City of Aberdeen John Milne 1911

GEOLOGY OF ABERDEEN

The Loch of Aberdeen had been a hollow in the bed of a glacier from Westburn Valley, which had received additions from Berryden and the howe between Spital and Sunnyside. Its course after passing through the bed of the Loch had been by St Nicholas Street and Carnegie's Brae to the Denburn, and it had helped to form the steep side of St Catherine's Hill on the west. During the time of snow and ice the Strait of Dover had been sometimes open and sometimes shut — open when the land was deep into the sea and shut when it had risen out of the sea. There is a peculiar kind of porphyry (Ignacious Rock) at Buchanness Lighthouse which is easily recognised where ever it is seen. Well-rounded pebbles of it are seen at the mouth of the Ythan, Girdleness, Bay of Nigg, Cove, Muchalls, Bervie Bay, and even as far south as Cambridge, telling of a southward movement of ice along the coast on the way to the Atlantic by the Strait of Dover. On the other hand there is evidence of a northward movement when the land ice was on its way to the Atlantic by the Orkney Isles, the Strait of Dover being dry or shallow. Old red sandstone pebbles from the conglomerate rocks of Kincardine are found in the clays on the south side of the Bay of Nigg, about Girdleness, and all along the east coast as far north as Buchanness. They are easily recognised by their red colour outside and whiter inside, and by crushed spots and cracks radiating from them, which they got by pressing on one another during movements of the earth's crust when lying in a bed of conglomerate. After the 25 feet beach was formed the land had risen again and had not stopped when it attained its present level, but had held on rising. The proof of this is that in deep excavations in the harbour for the foundations of Regent Bridge, and in a deep pit in the sea at the Bathing Station, beds of peat moss were found. These must have been formed after the ICE Age had passed away and while Aberdeen was farther above the sea level than it is now.  After the formation of the moss the land must have sunk till it reached its present level.

At the end of the glacial period the land had everywhere sloped gently to the sea, and the coast line had been farther out than it is now. Since then the sea has been gaining on the land and much of the loose matter carried into it by the snow sheet has been washed away into deep water. On both sides of Stonehaven grassy slopes may be seen suddenly terminating in rocky cliffs which had been at the waterline before the ice period came on. Even the solid rock is wasting away under the powerful action of the sea waves.  When the 25 feet beach was raised to its present level no part of the space between the Tile Burn and the sea had risen much above the level of the sea at high water, but there had been a broad area of dry sand at low tide. A vast amount of sand had in the course of time come down the Don, and it had been washed to the south side of the river mouth in north-east storms. In easterly gales sand had been blown inward from the broad area of dry sand and piled up into the high ridge of sand between the sea and the Tile Burn and the Banstickle Burn, which is no longer visible.

The snow was still entering the sea and was leaving stony clay above the stratified sand in some places. A good example of this may be seen at the north end of Muchalls Railway Station. But the snow sheet was breaking up and moving in streams and not with an unbroken front. Such hills as the Hermitage Hill and Tillydrone in Old Aberdeen, the Spital Hill, Broad Hill, Gallow Hill, Porthill, Heading Hill, Castle Hill, and St Fittock's Hill in Aberdeen are remnants left of the sand deposited when the sea margin was at 200 feet. The excavations in the Denburn Valley below Jack's Brae, in the Holburn Valley below Justice Mills, in the valley of the Pitmuckston Burn east of Holburn Street, Carnegie's Brae, Berryden, the hollow west of the Spital Hill, the bed of Old Aberdeen Loch — these and others such like were the work of the snow sheet reduced to narrow streams of ice called glaciers. St Catherine's Hill, now gone, stood in Union Street and was higher than the houses then round about. It was composed of layers of fine sand and could be accounted for in no other way than that it was a remnant left of a deposit of sand extending west to near Rubislaw Quarry.

SITUATIONS OF PREHISTORIC SETTLEMENTS
In forming an opinion whether a place had been the site of a prehistoric hamlet great regard should be paid to the presence or want of a perennial supply of good potable water. Since water is indispensable it is safe to say - no water, no people. That the prehistoric inhabitants of Scotland lived in communities near good water is known by their graves. They had two modes of internment - one in which a corpse was laid in the ground in a shallow grave, sometimes stone-lined, in the contracted posture in which the person died; another in which the dead body was burned and the ashes were collected and buried. The latter was the more common way - at least it is that of which traces are oftenest seen, though this may be owing to the complete decay, in long lapse of time, of an unburned body and the indestructibility of the fragments of charcoal mixed with the ashes of a body which had been burned. In digging drains and in ploughing the ground a little deeper than usual spots are met with where a small quantity of very black earth is turned up like that seen where a bonfire has been made. Such a spot marks the place where an interment of the ashes of a burned body has been made in a shallow round hole. Sometimes a few stones are found above the ashes ; often none. If a long stone could be procured it was set up to mark the grave. In the corner between Dee Street and Langstane Place there is a long stone marking a grave; another at one time stood near Hill Street; and there is a tall monolith marking a grave at Hilton near Stewart Park.

Sometimes the ashes are in an urn inverted and standing on a flat stone. Where one such grave is found there are usually many more. Such burial places are invariably in the vicinity of water suitable for drinking. The ancient people had not the means of conveying water and had to go where it was to be found. Given a warm, sunny spot near a river, a burn, or a lake, with the means of procuring food in the neighbourhood, we may with confidence look there for traces of a pre-historic community.  Another indispensable condition for primitive man was access to the sea in winter. With domestic animals to cultivate the ground in summer and produce food for us.  In winter man can maintain life in the interior of Scotland all the year round with comfort ; but without cattle and without access to the sea in winter men would have been unable to survive the frequent rigorous winters of Scotland. Both these essentials for primitive man — proximity to potable water, and convenient access to the sea — were at the command of the early settlers at the mouths of the Don and the Dee.

James Gordon - Map of Aberdeen 1661

No place could have been better adapted for being occupied by an uncivilised primitive people than the site of the nucleus of Aberdeen, on a plot of level ground about Shore Brae on the bank of the Denburn, which, after emerging from the valley now spanned by Union Bridge turned east in the line of the modern Guild Street, Trinity Quay, and Virginia Street. The high tide came up to the doors of the inhabitants, and they had the Denburn for their harbour. They had behind them on the north a high sheltering bank, extending from the Denburn valley along Gaelic Lane, the end of St Nicholas (Churchyard, St Nicholas Lane, Carnegie's Brae, Putachieside (now under Market Street), St Catherine's Hill, Castlegate, Castle Hill, and the Heading Hill. Beyond the burn there lay on the south the Inches — a broad expanse of sand and mud brought down by the Dee, forming one side of their harbour ; and beyond these flowed the Dee, nearly in its present course — perhaps a little farther south. Around the mouth of the Dee there was good fishing ground, and the river itself abounded in trout and salmon. The rocky coast south of the Dee yielded an unfailing supply of dulse (Edible Sea Weed) and shell-fish, important items in the diet of early man.

Recent explorations have carried back civilisation in Egypt and Assyria thousands of years before Christ. Civilisation in Scotland came much later, but thousands of years ago Scotland was as well adapted for being the abode of a primitive people as when civilisation began, and we need have no hesitation in ascribing to the earliest settlement on the bank of the Denburn a very high antiquity.  About the beginning of last century traces of man were found in making excavations in the site of the harbour.  A piece of flint, two skulls, and numerous shells were found at 20 feet below sea level. Both the flint and the shells indicate that it is a very long time since the owners of the skulls lived.

If the Romans visited Aberdeen they have left no trace behind them. Ptolemy's tables of names and longitudes and latitudes are disappointing and give no real useful information on the subject. But Aberdeen was not quite inaccessible before the Bridge of Dee was built. A road from the south, called the Causey of the Cowie Munth, crossed the east end of the Grampians, and, coming down by Kincorth, crossed the Dee by a ford at Pitmuckston, where there seems to be a shelf of rock ground flat by the Dee glacier. There was also a ferry at Craiglug for foot passengers.

 


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Last modified: 01/09/2013