Fir Island sitting in Carlingwark Loch, Castle Douglas is relativly small. There are local traditions that the island may have been the home of a small Chapel, but there are no remains visible on the Island.
In the 1st Statistical account of Scotland published in the 1790’s (vol III 297-307) the write of the Kelton account states :
“There was always a tradition in the parish, that there had been a town in the loch, which sunk, or was drowned; and that there were two churches or chapels, one on each of the two large isles”
The other isle mentioned is probably Ash Island.
Other references:
Canmore link: http://canmore.org.uk/site/64675/fir-island
Places of Worship in Scotland link: http://scottishchurches.org.uk/sites/site/id/9718
View a location map: View Fir Island on gridreferencefinder.com
Images: