The Wee Thing referred to in the song is Mary from Castlecary, a small, historic, village in North Lanarkshire, Scotland.
'I saw na your wee thing, I saw na your ain thing,
Nor saw I your true love down by yon lea;
But I met a bonnie thing, late in the gloaming,
Down by the burnie whare flowers the haw-tree.
Her hair it was lintwhite, her skin it was milkwhite;
Dark was the blue o' her saft rolling e'e;
Red were her ripe lips, and sweeter than roses;
Sweet were the kisses that she gae to me.'
'It was na my wee thing, it was na my ain thing,
It was na my true love ye met by the tree:
Proud is her leal heart, and modest her nature,
She never lo'ed ony till ance she lo'ed me.
Her name it is Mary, she's frae Castlecary;
Aft has she sat, when a bairn, on my knee.
Fair as your face is, were't fifty times fairer,
Young bragger, she ne'er wad gi'e kisses to thee.'
'It was then your Mary; she's frae Castlecary;
It was then your true love I met by the tree.
Proud as her heart is, and modest her nature,
Sweet were the kisses that she ga'e to me.'
Sair gloomed his dark brow, blood-red his cheek grew,
And wild flashed the fire frae his red-rolling e'e;
'Ye'se rue sair this morning your boasts and your scorning,
Defend ye, fause traitor! fu' loudly ye lee!'
'Awa' wi' beguiling!' cried the youth smiling:
Aff went the bonnet, the lintwhite locks flee;
The belted plaid fa'ing, her white bosom shawing,
Fair stood the loved maid with the dark rolling e'e.
'Is it my wee thing? is it my ain thing?
Is it my true love here that I see?'
'Oh Jamie, forgi'e me! your heart's constant to me.
I'll never mair wander, dear laddie, frae thee.'