Letter to Susan Prescott
p154“I am studying Madame de Stael, Epictetus, Milton, Racine, and Castilian ballads, with great delight.”
Fuller, Margaret. The Letters of Margaret Fuller. Edited by Robert N. Hudspeth. Vol. I. Ithaca: Cornell University Press, 1983.
Inferred Fuller refers to "Castilian ballads"; Hudspeth identified this as probably John Gibson Lockhart's Ancient Spanish Ballads, Historical and Romantic.
The attribution is marked probable because Hudspeth himself uses the qualifier "probably."