The term 'seamy stuff' refers to the dark, unpleasant side of something. In this case, it is referring to the mining of ORE, COAL, and ores. ORE is a mineral or rock from which a valuable metal or mineral can be extracted. COAL is a combustible black or brownish-black sedimentary rock, formed by the partial decomposition of plant material. Ores are rocks or minerals from which a valuable metal or mineral can be extracted. All three of these materials are mined in order to be used for various purposes.