Green’s Dictionary of Slang

blarnation n.

(US) idle chatter; nonsense.

1837		E.H. Barker Literary Anecdotes (1852) 170: Lord Brougham.—Most musical nation! that's what I call (Aside.) blarnation.
1880		Dly Globe (St Paul, MN) 3 June 1/1: The evening had been given over to committees, caucusing and general blarnation.

In exclamations

blarnation!

(US) nonsense!

1865

G.A. Sala My Diary in America II 288: ‘Never!’ cried the drowning man. ‘Blarnation! Nary ticket. Cast me loose.’ He preferred a watery grave to the tyranny of the Camden and Amboy Railroad.