the Silesian Upland. The coalfield has an area of about . Deposits in Lower Silesia have proven to be difficult to exploit and the area's unprofitable mines were closed in 2000. In 2008, an estimated 35 billion tonnes of lignite reserves were found near Legnica, making them some of the largest in the world. From the fourth century BC, iron ore has been mined in the upland areas of Silesia. The same period had lead, copper, silver, and gold mining. Zinc, cadmium, arsenic, and uranium have also been mined in the region. Lower Silesia features large copper mining and processing between the cities of Legnica, Głogów, Lubin, and Polkowice. The region is known for stone quarrying to produce limestone, marl, marble, and basalt. The region also has a thriving agricultural sector, which produces cereals (wheat, rye, barley, oats, corn), potatoes, rapeseed, sugar beets and others. Milk production is well developed. The Opole Silesia has for decades occupied the top spot in Poland for their indices of effectiveness of agricultural land use. Mountainous parts of southern Silesia feature many significant and attractive tourism destinations (e.g., Karpacz, Szczyrk, Wisła). Silesia is generally well forested. This is because greenness is generally highly desirable by the local population, particularly in the highly industrialized parts of Silesia. Demographics Silesia has been historically diverse in every aspect. Nowadays, the largest part of Silesia is located in Poland; it is often cited as one of the most diverse regions in that country. The United States Immigration Commission, in its Dictionary of Races or Peoples (published in 1911, during a period of intense immigration from Silesia to the United States), considered Silesian as a geographical (not ethnic) term, denoting the inhabitants of Silesia. It is also mentioned the existence of both Polish Silesian and German Silesian dialects in that region. Ethnicity Modern Silesia is inhabited by Poles, Silesians, Germans, and Czechs. Germans first came to Silesia during the Late Medieval Ostsiedlung. The last Polish census of 2011 showed that the Silesians are the largest ethnic or national minority in Poland, Germans being the second; both groups are located mostly in Upper Silesia. The Czech part of Silesia is inhabited by Czechs, Moravians, Silesians, and Poles. In the early 19th century the population of the Prussian part of Silesia was between 2/3 and 3/4 German-speaking, between 1/5 and 1/3 Polish-speaking, with Sorbs, Czechs, Moravians and Jews forming other smaller