Northumberland
The imposing Northumberland landscape is hugely diverse. It includes the long swathes of sandy beaches of the North Northumberland Heritage Coast, the upland scenery and the Cheviot massif of the Northumberland National Park, and the pastures and river valleys of the south.
The Whin Sill, which dominates large areas of the northern English landscape, was once a hot liquid rock, as shown by the ropy flow texture of the rock here
This diverse landscape is characterised by the underlying geology, which is principally composed of sedimentary rocks of Carboniferous age but also igneous rocks that include the widespread intrusions of the Whin Sill and the igneous complex of the Cheviot Hills, the remains of a Devonian volcano.
Devonian
The Cheviot Hills dominate the landscape in the north of the Northumberland National Park. These rocks are the remnants of volcanic activity and are the oldest rocks in the region of possible lower Devonian age (380-million-years-old). The geology of the hills can be related to a series of stages of igneous activity. An initially explosive volcano was followed by a large out-pouring of lava, which today covers an area of 600 km2. This large area of lava was then intruded at depth by a mass of granite which today, revealed by erosion, forms the highest parts of the Cheviot Hills.
Carboniferous
Carboniferous rocks (345 to 280-million-years-old) dominate the underlying geology, with the exception of the igneous complex of the Cheviot Hills. In addition to providing the framework to much of the Northumberland landscape, these rocks have also played a vital role in the history and economics of the area through many centuries of exploitation.
The oldest rocks of the area belong to the Carboniferous Limestone Series. These rocks are composed of thinly bedded sandstones, mudstones and limestones deposited in a marine to estuarine environment, and outcrop in the north and north east of the county.
The Carboniferous Limestone is overlain by the Millstone Grit Series, which occupies the south west and central east of the county. In Northumberland, the Millstone Grit Series consists of a sequence of limestones, shales and sandstones, and the ‘Millstone Grit’ itself, thick coarse-grained sandstones, siltstones and mudstones. These rocks were deposited in the late Carboniferous (approximately 300 million years ago) in a coastal environment where large river deltas were building out into the shallow marine waters. Continuing deposition over the millennia led to the further building out of the deltas and the formation of extensive low-lying, swamps.
The overlying Lower and Middle Coal Measures dominate the geology of southern Northumberland. The rocks of the Coal Measures show a repeated coal, sandstone and mudstone cycle which reflects relative changes in land and sea level. The coals represent the fossilised remains of swamp vegetation which grew as luxuriant forests on the deltas, while the mudstones were deposited under shallow marine conditions. The Coal Measures were heavily exploited by man until the gradual decline of the coal and steel industries from the 1930’s onwards.
The igneous intrusions of the Whin Sill are present at a number of locations across Northumberland. The Whin Sill exerts an important influence on the landscape, often creating dramatic and striking scenery. The sea cliffs of the Farne Islands and the land underlying Bamburgh Castle are two examples of this.
Quaternary
Over the last two million years the climate of Britain has varied tremendously with periods of temperate climate interrupted by repeated advances and retreats of glaciers and ice sheets. Collectively these periods have become known as the Ice Age (we are still in one of the temperate phases) and the actions of the ice sheets have been instrumental in forming the landscape we see today.
The majority of the underlying geology of Northumberland is covered by a thick layer of sediments deposited during the last main glacial period of the Ice Age. Most of these deposits are tills (boulder clay), with small areas of sands and gravels centred around existing rivers and small patches of clay deposited in glacial lakes.
Geological highlights:
- Coal has been worked in Northumberland since at least the early 13th century. For many centuries coal was mined on a relatively small scale, primarily for domestic use, and for the local salt industry. During the 18th and 19th centuries, improved technology allowed deeper pits to, greatly increasing coal production and making it one of the richest coal mining regions of the country. The coal industry provided a tremendous stimulus to urban development and heavy industry across south-east Northumberland and most of the county’s 120 mines were located within this area. In the 1950s and 1960s, the decline of deep mining was rapid, and today open cast mining continues at several large sites, but the only remaining deep pit is at Ellington, the workings of which are mainly beneath the sea.
- The Whin Sill outcrops in a series of dramatic and rugged north facing escarpments across the south of Northumberland. The series of east-west oriented ridges formed by the Sill were exploited by the Romans, who, in AD122, started the construction of the117km long Hadrian’s Wall between Wallsend in the east and Bowness-on-Solway in the west. Hadrian’s Wall was declared a World Heritage Site in 1987.
- The Cheviot Hills form part of the wild upland plateaux of Northumberland moors which continue northwards across the Scottish border. The granite summit is characterised by areas of wet acidic blanket bog and patches of heather in drier areas. The volcanic rocks typically weather to form rounded hills, but a few craggy outcrops of more resistant lava occur on some hilltops and ‘tors’ of granite are found on some hills notably Great and Little Standrop. The Cheviots also display many typical glacial and post-glacial features. The curious hollows of Bizzle and Henhole are cirques or corries carved out of the north face of the hills by glacial scouring. Water from melting ice cut the meltwater channels seen today below Yeavering Bell.
- A prominent lens-shaped intrusion of brick-red fine-grained granite within the Cheviot Hills complex has long been quarried for roadstone at Biddlestone near Alwinton. This is known as the 'Red Whin', and is an attractive red stone that has been used to line The Mall in London and to demarcate many motorway 'hard shoulders' across Britain.
- The North Northumberland Heritage Coast stretches 40 miles from Amble to the Scottish border. The coast provides exposure through much of the Carboniferous rock succession of the county and exhibits some impressive coastal features and forms. The coast is characterised by long stretches of sandy beaches, sand dunes, tidal mudflats and cliffs and headlands. At Lindisfarne many different coastal forms are present including one of only four barrier beach systems in England and Wales.
Local sites
The following localities represent, in part, the geology of this county. Each locality has a grid reference, a brief description of how to get there and a short summary of the geology you are likely to find. All the localities listed are openly accessible.
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