Next a smoky fog of clouds covered the whole region densely, and we took to the railway ties to keep from getting lost. Sometimes we slopped along in a narrow path on the left-hand side of the track, but by and by when the fog blew aside a little and we saw that we were treading the rampart of a precipice and that our left elbows were projecting over a perfectly boundless and bottomless vacancy, we gasped, and jumped for the ties again.
Mark Twain “A Tramp Abroad. Vol. I” London 1880