Green’s Dictionary of Slang

(US) thus, to sum things up.

1865		Harper’s Mag. Dec. 133/2: It happened, as J. Billings would say, ‘thusly’ .
1876		Pioche Jrnl (NV) 23 Sept. 3/1: The latest thing in the way of a soul-warmer that the youths of Pioche have got is a dingis made thusly [OED].
1889		Boston Jrnl (MA) 17 Jan. 2/3: On his way home George mused thusly .
1893		Lady Burton Life Sir R.F. Burton 3: Stories never lose anything in the recital, and consequently this one grew thusly .
1909		J. Ware Passing Eng. of the Victorian Era.