Sentence:  This pathway ran up hill, across another open space covered with white incrustation, and plunged into a canebrake again. Then suddenly it turned parallel with the edge of a steep-walled gap, which came without warning, like the <WSD>ha-ha</WSD> of an English park,—turned with an unexpected abruptness. I was still running with all my might, and I never saw this drop until I was flying headlong through the air. 
Meaning of the word marked with <WSD> tags:  A ditch with one vertical side, acting as a sunken fence, designed to block the entry of animals into lawns and parks without breaking sightlines.