After a rainstorm in December 1916, South Uist awoke to find their white cattle turned completely black. The rains had coated everything on the island with “a strange black dust like burnt gunpowder”.
The press gave no explanation at the time as to what the source of the strange “burnt gunpowder”. Suggestions from Twitter followers were industrial pollution from the Central Belt and battle dust from the fighting in France. The winds were strong from the Southeast that night so both ideas are plausible.