Complex sentence: The coming of the railways enabled the locally mined coal to be sent across the country, demand soon outstripped supply and many more shafts were sunk to reach the rich coal seams under the town.
Split into simpler sentences: The coming of the railways enabled the locally-mined coal to be sent across the country. Demand soon outstripped supply and many more shafts were sunk to reach the rich coal seams under the town.