blacken

Iron and coal were the magnets that drew railways to this land of lovely valleys and silent mountains—for such it was a century-and-a-half ago, before man blackened the valleys with the smoke of his forges, scarred the green hills with his shafts and waste-heaps, and drove the salmon from the quiet Rhondda and the murmuring Taff.

The sky blackened as the storm clouds rolled in.