The Longy spring

Because water seems to rise from the ground for no reason, springs are often thought to possess a spiritual and magical character. They are called the Bonnes Fontaines - good springs - in the Limousin because they are said to have healing qualities. They are also said to be Christianised because they often corresponded to ancient Celtic places of worship. A healing saint was attributed, and a cross was erected in the immediate vicinity. Very little is known about the Longy spring: which saint was attributed to it? What healing virtue was associated with it?