River Wear - Geology and History

Geology and History

The Wear rises in the east Pennines, an upland area raised up during the Caledonian orogeny. Specifically, the Weardale Granite underlies the headwaters of the Wear. Devonian Old Red Sandstone in age, this Weardale Granite does not outcrop but was surmised by early geologists, and subsequently proven to exist as seen in the Rookhope borehole. It is the presence of this granite that has retained the high upland elevations of this area (less through its relative hardness, and more due to isostatic equilibrium) and accounts for heavy local mineralisation, although it is considered that most of the mineralisation occurred during the Carboniferous period. Mining of lead ore has been known in the area of the headwaters of the Wear since the Roman occupation and continued into the nineteenth century when it accounts for the early extension of the then-new railways westwards along the Wear valley. Fluorspar is another mineral sporadically co-present with Weardale Granite and became important in the manufacture of steel from the late c19 into the c20; in many cases the steel industries were able to take previously unwanted excavation heaps. Fluorspar explains why iron and steel manufacture flourished in the Wear valley, Consett and Teesside during the nineteenth century. Overlying are three Carboniferous minerals: Limestone, Coal Measures as raw materials for iron and steel manufacture, and sandstone, useful as a refractory material. The last remaining flourspar mine closed in 1999 following legislation re water quality. A mine at Rogerley Quarry Frosterley is operated by an American consortium who occasionally work it for specimen minerals. Minco are currently exploring the North Pennines and the upper Wear catchment for potential reserves of zinc at lower levels. Ironstone which was important as the ore was won from around Consett and Tow Law, then around Rookhope, while greater quantities were imported from just south of the southerly Tees in North Yorkshire. These sources were in due course depleted or became uneconomic. Spoil heaps from the abandoned lead mines can still be seen, and since the last quarter of the twentieth century have been the focus of attention for the recovery of gangue minerals in present mining, such as fluorspar for the smelting of aluminium. However, abandoned mines and their spoil heaps continue to contribute to heavy metal mineral pollution of the river and its tributaries. This has significance to fishing in times of low flow and infrastructure costs as the River Wear is an important source of drinking water for many of the inhabitants along its course. The former cement works at Eastgate, until recently run by Lafarge, was based on an inlier of limestone. The site recently gained planning permission to form a visitor complex show casing and eco village using altenative technology including "hot rocks" water heating system. The underlying granite has been drilled and reports confirm their presence. Bardon Aggregates continue to quarry at Heights near Westgate and operate a tarmac "blacktop" plant on site.

Mineral extraction has also occurred above St John's Chapel with the extraction of Ganister which was used in the steel process at Consett. Around Frosterley, Limestone, Sand (crushed sandstone) and Frosterley Marble http://en.wikipedia.org/wiki/Frosterley have been worked and the Broadwood Quarry recently expanded into ground held on an old licence. The crushing plant continues to operate. A quarry at Bollihope was also mooted on a similar basis but plans seem to have been discontinued. Frosterley Marble was used extensively in church architecture, there are local examples in St Michael's church Frosterley and Durham Cathedral.

The upland area of Upper Weardale retains a flora that relates, almost uniquely in England, to the end of the last Ice Age, although it almost or entirely lacks the particular rarities that make up the unique "Teesdale Assemblage" of post-glacial plants. This may, in part, be due to the Pennine areas of Upper Weardale and Upper Teesdale being the site of the shrinking ice cap. The glaciation left behind many indications of its presence, including lateral moraines and material from the Lake District and Northumberland, although surprisingly few drumlins. After the Ice Age, the Wear valley became thickly forested, however during the Neolithic period and increasingly in the Bronze Age, were largely deforested for agriculture — many woods break up rolling fields and crags in Weardale but not on the scale of for instance in the region Kielder Forest partly in Northumberland National Park.

It is thought that the course of the River Wear, prior to the last Ice Age, was much as it is now as far as Chester-le-Street. This can be established as a result of boreholes, of which there have been many in the Wear valley due to coal mining. However, northwards from Chester-le-Street, the Wear may have originally followed the current route of the lower River Team. The last glaciation reached its peak about 18,500 years ago, from which time it also began a progressive retreat, leaving a wide variety of glacial deposits in its wake, filling existing river valleys with silt, sand and other glacial till. At about 14,000 years ago, retreat of the ice paused for maybe 500 years at the city of Durham. This can be established by the types of glacial deposits in the vicinity of Durham City. The confluence of the River Browney was pushed from Gilesgate (the abandoned river valley still exists in Pelaw Woods), several miles south to Sunderland Bridge (Croxdale). At Chester-le-Street, when glacial boulder clay was deposited blocking its northerly course, the River Wear was diverted eastwards towards Sunderland where it was forced to cut a new, shallower valley. The gorge cut by the river through the Permian magnesian limestone can be seen most clearly at Ford Quarry.

In the 17th edition of Encyclopædia Britannica (1990), reference is made to a pre-Ice Age course of the River Wear outfalling at Hartlepool.

Much of the River Wear is associated with the history of the Industrial Revolution. Its upper end runs through lead mining country, until this gives way to coal seams of the Durham coalfield for the rest of its length. As a result of limestone quarrying, lead mining and coal mining, the Wear valley was amongst the first places to see the development of railways. The Weardale Railway continues to run occasional services between Stanhope and Wolsingham.