Wolf-hunting and wild sport in lower Brittany, by EWL Davies and published in 1875, contains, naturally enough, some discussion of the Breton language, but also offers a couple of references to Jèrriais:

The man’s countenance, however, had more of the knave than the ruffian in it, with something about the glint of his eye, expressive at once of broad humour and intense cunning. I was so attracted at first by his extraordinary costume that for some moments I did not observe his face ; but when at length I looked up and caught his eye, and then heard him address St. Prix in that broad franc-patois peculiar to Jersey, I immediately recognised the individual as a livery-stable keeper, with whom I had had occasional dealings during my sojourn in that island. He, too, recognised me, and lost no time in making the fact known by asking how a bay horse had turned out that he had sold me the last time I had visited his stables. ” I have come to this country,” he said, ” to attend some horse-fairs at Rostrenan, Chateaulin, and Morlaix ; and, with a bit of luck, I hope to pick up a string of useful cobs that will sell well at Southampton ; for, that is my market now, not St. Hellier’s, where a lot of fellows have congregated who can’t afford to pay for a pint of shrimps.”

(…)

Some hours elapsed ere an answer was returned by Johnson, but at length it came, written fluently in Jersey-French, and expressing his gratitude in terms so extra-deferential, that St. Prix could not forbear shrugging his shoulders as he read it; as if there was something beyond his comprehension, something very unlike the independent manner of an English gentleman in the whole style of the note.