together produced around 600 million tonnes of coal when the cabinet of Jo Cals decided to completely close down coal production in the province of Limburg, and the then minister of economic affairs, Joop den Uyl, decided to make a personal visit to the mining centre of Heerlen to announce his decision. A natural gas field had been discovered in the province of Groningen, a gigantic reservoir of clean energy that would be much cheaper to exploit than coal from Limburg, which by then had to be fetched to the surface from a depth of over 800 metres. Impact of the mining industry In three quarters of a century the mining industry had drastically altered the eastern corner of South Limburg in every aspect. When the first pitheads were built, this was an agricultural region of small villages with a population of scarcely 22,000. By the time the mines were closed down, more than ten times as many people lived there, and it was one of the most densely populated parts of the Netherlands, second only to the Randstad, the urban agglomeration in the western part of the country. The mining industry had attracted a host of supply industries and an excellent infrastructure of railways and canals had been built to facilitate the transport of coal to domestic and foreign markets. The Juliana Canal was constructed for this purpose in the years 1925-1936, and in the same period a 13 kilometer long railway line was built between Schaesberg and Simpelveld to cater for daily passenger traffic. This line became known as the 'million line', because it cost more than a million guilders per kilometre of track to lay it, a record sum for those days. The most far-reaching changes, however, took place at the social level. There was a massive influx of workers to take up jobs in the mines. They came not only from all corners of the Netherlands, but also from older mining areas in Germany, Poland, Italy, Spain, Morocco and elsewhere. In 1939 almost 700 foreigners of nine different nationalities lived in Kerkrade, which had become the largest mining town in Europe. Mine management began to build houses for their workforce at an early stage, so that mineworker colonies arose, such as that at Lutterade near Geleen. Because there were numerous social problems in the mining area, and most of the miners were Roman Catholic, the bishop