The Durham coalfield was one of the most prolific in England. The Coal Measures with their coal seams were exposed at the surface immediately east of the slopes of the North Pennines in a north-south band through the centre of the county. It was is this area that the earliest mining developed with the digging of small pits and adits or tunnels directly into the seams. The seams tilted down gently towards the east, and as resources at or near the surface became expired mining moved gradually eastwards towards the coast, reaching the coal via ever-deepening shafts, and eventually extracting coal from seams far out under the North Sea.
Probably from before the 16th century Durham coal served major markets round the North Sea, not least London and the Low Countries. With mining concentrated in the eastern parts of the county the problem of access to the sea or the county's major rivers for shipment was a major obstacle to overcome. In early years transport would have been packhorse, but the problem drove technical innovation during the 18th century with the development of engineered wooden waggonways along which "chaldron" wagons would be horse drawn, or travel under the power of gravity, to the points of loading into the colliers, the coal-carrying vessels which would take the coal to the markets.
In turn, in the early 19th century, waggonways were developed into railways, not too different in basic concept to those we know today, and powered by the steam locomotives which were also developed within the region. The first of these public railways was the Stockton & Darlington Railway, opened in 1825, specifically to transport coal from South Durham around Bishop Auckland to the River Tees for shipment, and so creating the port of Middlesbrough.
Durham coal was of a very high quality and very suitable for conversion into coke, which was the fundamental fuel for the smelting of iron in the blast furnaces being constructed to provide the principal material for many of the new products of the industrial revolution. One of the rapidly developing centres of the Iron industry was the Furness area of Lancashire, where rich iron ore deposits were geographically remote from supplies of coal and coke. West Cumberland, too, was another centre for development of the industry, and although there were plentiful supplies of local coal, this was not ideal for iron smelting.
With the opening of the South Durham and Lancashire Union Railway in 1861, and the Eden Valley and Cockermouth Penrith & Keswick Railways a few years later, the colliery owners of South Durham were rapidly able to take up the new markets. Extensive coke ovens were built at or near the major collieries to convert coal into coke, and the coke despatched in hopper wagons to the iron and steel works in what is now Cumbria. At its peak in the late 19th century this traffic would reach over one million tons a year travelling over Stainmore to the iron works of Furness and West Cumbria. It would continue until the furnaces at the large iron and steel works in Barrow were taken out of blast about 1960.