legacy of this, with all its major cities being current or former centres of various forms of manufacturing. However, this in turn was built on its exploitation of natural resources, especially coal and iron ore. Primary industry The UK's primary industry was once dominated by the coal industry, heavily concentrated in the north, the Midlands and south Wales. This is all but gone and the major primary industry is North Sea oil. Its activity is concentrated on the UK Continental Shelf to the north-east of Scotland. Manufacturing The UK's heavy manufacturing drove the industrial revolution. A map of the major UK cities gives a good picture of where this activity occurred, in particular Belfast, Birmingham, Glasgow, Liverpool, London, Manchester, Newcastle and Sheffield. Today there is no heavy manufacturing industry in which UK-based firms can be considered world leaders. However, areas of the UK still have a notable manufacturing base, including the Midlands which remains a strong manufacturing centre, and the North West which accounts for 60% of the United Kingdom's manufacturing output. More recently, high technology firms have concentrated largely along the M4 motorway, partly because of access to Heathrow Airport, but also because of agglomeration economies. Finance and services Once, every large city had a stock exchange. Now, the UK financial industry is concentrated overwhelmingly in the City of London and Canary Wharf, with back office and administrative operations often dispersed around the south of England. London is one of the world's great financial centres and is usually referred to as a world city. There is also a significant legal and ebusiness industry in Leeds. Regional disparity The effect of changing economic fortune has contributed to the creation of the so-called North-South divide, in which decaying industrial and ex-industrial areas of Northern England, Scotland and Wales contrast with the wealthy, finance and technology-led southern economy. This has led successive governments to develop regional policy to try to rectify the imbalance. However, this is not to say that the north–south divide is uniform; some of the worst pockets of deprivation can be found in London, whilst parts of Cheshire and North Yorkshire are very wealthy. Nor is the North-South divide limited to the economic sphere; cultural and political divisions weigh heavily too. Natural resources Historically, much of the United Kingdom was forested. Since prehistoric times, man has deforested much of the United Kingdom. Agriculture is intensive, highly mechanised, and efficient