It was a maiden assize.
"Life of Johnson" by James Boswell
Limb of the Law on a maiden assize and white gloves, 29.
"Notes & Queries, Index of Volume 1" by Various
Assize, maiden, at Norwich, 231.
"Norfolk Annals A Chronological Record of Remarkable Events in the Nineteeth Century, Vol. 2" by Charles Mackie
Maiden assizes are any thing but uncommon in that country.
"Blackwood's Edinburgh Magazine, Volume 63, No. 391, May, 1848" by Various