WOOL-Gathering,
as, Your Wits are a Wool gathering; said of a Person in a serious, or, as 'tis called, in a brown Study; or who knows not what he does.
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Entry taken from 1736 Canting Dictionary, by Nathan Bailey.
Wool Gathering in the 1811 Vulgar Tongue
Also see examples in Canting Songs and Slang Rhymes collected by John S. Farmer (1896).