The film tells the history of coal mining from the eleventh century until the present day. As digging developed and the original excavations became deep and extensive galleries, the hazards of flood, fire and poisonous fumes were added to an already arduous and dangerous occupation. Only gradually did inventors produce the means of combating these. While following these technological developments the film gives equal attention to the human factor, particularly during the period when women and children were employed in deep mines. A tremendous amount of research has gone into the preparation of the script, the early mining scenes are convincingly represented and contemporary illustrations are used for some later scenes. The music is especially notable in establishing the atmosphere.