The great cities that surround the Pennine Chain form four groups: first, those of Northumberland and Durham with Newcastle as the main center; second, those of the great county of Yorkshire including Leeds and Sheffield; third, those of the Midlands in the five counties of Nottingham, Derby, Leicester, Warwick, and Stafford at the southern end of the Chain with Birmingham as the greatest city; and fourth, those of Lancastria including the counties of Cheshire and Lancashire and the great city of Manchester. The basic connection between these four groups of cities is of course the coal, but the fact that the wool of the Pennine Hills long ago stimulated primitive manufacturing in the valleys leading down from the hills must not be overlooked.
Newcastle, the most northerly of the great English cities, lies on the Tyne River between Northumberland and Durham. In many ways it is much like Cardiff in Wales at the other end of the British industrial section. Its good harbor near the mouth of the Tyne, and the low Tyne gap which gives easy access to the west coast, have always made the place important, but its main growth is due to the presence of coal almost at the water's edge. With the increasing demand for coal in London and other parts of eastern England, as well as on the continent of Europe, Newcastle has forged steadily ahead. Conditions like those at Glasgow, combined of course with Britain's insularity, its western position, and the fishing industry, have led to a large ship-building industry. This in turn has stimulated many kinds of iron work including the making of machinery not only for ships, but for mines, railways, and other purposes. Around the coalmines and in such neighboring cities as Gateshead and South Shields at the mouth of the Tyne important metal and chemical industries have grown up. They use iron ore brought from the Tees Valley, a little farther south, or from Spain and Sweden; pyrites from Spain; and salt from all sorts of places.
Sunderland at the mouth of the Wear River a little southeast of Newcastle has had a simpler development. Coal is the main export, and timber for mines is an important import. Like Newcastle, Sunderland has a number of shipyards. Middlesborough, still farther south at the mouth of the Tees, is still another center belonging to the Newcastle region. Although it is farther than the other centers from coal deposits, it has the advantage of being close to the iron ore of the Cleveland district. This explains the special importance of the smelting of iron ore and the export of pig iron to the other metal-manufacturing regions. The presence of salt in the neighboring Triassic strata is the basis for a progressive chemical industry.