Sentence:  The <WSD>fogfall</WSD> that lay along the crest in a cottony roll was as white as the clouds of a fairytale. Only the heads of the men in the skip were visible from where she stood just outside the door of the shaft house. 
Meaning of the word marked with <WSD> tags:  An instance (i.e. a cloud) of fog that has fallen or developed over an area.