The "Cranken Rhyme" is a Cornish-language song known by farmer John Davey (1812–1891), who was one of the last people with some knowledge of the tongue.
It was first published by Celticist John Hobson Matthews in his History of St. Ives, Lelant, Towednack, and Zennor, and is probably the latest known work of oral poetry in Cornish to be collected after the official language death.
[1] Either way, the song is unknown from any other source, demonstrating that Davey had knowledge of some original Cornish in the late 19th century.
However, Robert Morton Nance respelled the song into a recognizable form and provided an English translation.
It is evidently a bit of humour claiming that even the Penzance-Marazion road was more fertile than Cranken's stony fields.