TERRA-Firma,
an Estate in Land; Has the Cull got any Terra Firma? Has the Fool got any Land.
· 
· 
Entry taken from 1736 Canting Dictionary, by Nathan Bailey.
· ·
Terra Firma in the 1811 Vulgar Tongue
Also see examples in Canting Songs and Slang Rhymes collected by John S. Farmer (1896).