Sentence:  The road was scarcely passable; there were no longer cheerful farms and clearings, but the dark pine forest, and the rank swamp, crossed by those terrific corduroy paths (my bones ache at the mere recollection!) and deep holes and pools of rotted vegetable matter, mixed with water, black, bottomless <WSD>sloughs of despond</WSD>! The very horses paused on the brink of some of these mud-gulfs, and trembled ere they made the plunge downwards. 
Meaning of the word marked with <WSD> tags:  A dreary bog or marsh.