Amos,

"Rocking the Cradle" is a British broadside of wide distribution. It's not necessarily any more Irish than "The Newry Highwayman," which overlays Irish place names on a core story that's obviously set in London. "The Unfortunate Rake," too, is first known from an English source. Since English descendants were in Texas before great numbers of Irish immigrants arrived, there's no way to demonstrate if "Streets of Laredo" or "Git Along Little Dogies" has anything to do with Ireland or "the Celts" per se. But clearly there's an affinity between Texas music and what we think of as "Celtic" music nowadays.

A good example with perhaps a clearer connection. "The Devil Made Texas" (aka "Hell in Texas") is a song that originally appeared on broadsides throughout the Southwest. Though the early broadsides don't suggest a tune, when the song was sung it was often to the old jig "The Irish Washerwoman." You can hear Hermes Nye do it on the album "Cowboy Songs on Folkways." The selection of tunes clearly shows an Irish influence in the region, though the words have no obvious connection to ireland.

Another great resource, by the way, would be Ed Miller in Austin, an Edinburgh native, folklorist, and great singer of folk songs. He's recorded "Hell in Texas" on one of his CDs.