He skulks about the wharves of Joppa, and seeks a ship that's bound for Tarshish.

There lurks, perhaps, a hitherto unheeded meaning here.

By all accounts Tarshish could have been no other city than the modern Cadiz.

That's the opinion of learned men.

And where is Cadiz, shipmates?
Cadiz is in Spain; as far by water, from Joppa, as Jonah could possibly have sailed in those ancient days, when the Atlantic was an almost unknown sea.