Here's an insightful quote from the previously reviewed A JOURNEY IN THE SEABOARD SLAVE STATES Frederick Law Olmsted, 1856, that I don't believe we mentioned earlier. Pg. 26:

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He concluded by throwing a handful of earth on the coffin, repeating the usual words, slightly disarranged, and then took a shovel, and, with the aid of six or seven others, proceeded very rapidly to fill the grave. Another man had, in the mean time, stepped into the place he had first occupied at the head of the grave; an old negro, with a very singularly distorted face, who raised a hymn, which soon became a confused chant—the leader singing a few words alone, and the company then either repeating them after him or making a response to them, in the manner of sailors heaving at the windlass. I could understand but very few of the words. The music was wild and barbarous, but not without a plaintive melody.
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In several places in the book, Olmsted refers to African-American singing as "wild." We are also familiar with "plaintive." Here, however, he is making a comparison between this singing and and the singing of sailors at the windlass.