The question also makes its way into the song "Birmingham Sunday" by Richard Farina, as this verse (slightly altered from the above version):

The men in the forest, they asked it of me
How many blackberries grew in the blue sea
And I asked them right with a tear in my eye
How many dark ships in the forest

Link to the complete lyrics of "Birmingham Sunday" from the DT: /@displaysong.cfm?SongID=653