The most important characteristic feature of the unity and growing power of the world system of socialism is the international socialist division of labor. It enables each socialist country to rely not only on its own resources, but also on the vast raw material and fuel wealth of the entire world system of socialism.The Polish People's Republic ranks second (after the Soviet Union) in coal production among the socialist countries of Europe. Coal reserves in the Republic exceed those of all other European countries of people's democracy put together. The general geological reserves (up to the depth of 1000 m) are defined as 76-82 billion tons and are concentrated on the territory of two districts: Silesian-Krakowski and Lower Silesian. The Silesian-Kraków district accounts for 99% of all reserves, and the Lower Silesian district - only 0.9%, but of high quality coking coal. A total of 81 deep and 55 shallow mines are exploited in the country. The average depth of the mines does not exceed 250 m.