The Origins?
As Bruce said in the beginning...The great Robert Tannahill wrote it. It is interesting to note that it is one of the few songs by Robert Tannahill wrote that the Tannahill Weavers have recorded. It is kind of like forming an American folk group called "The Guthrie Singers" and never singing any Woody Guthrie songs. But I suppose that they named the group as an homage to the great scottish songwriter, not as a group that covers his music.

Bruce- Are you sure that "wild Mountain Thyme" is irish? I thought it was also Scottish. I have always seen it listed as Scottish. I have seen "Wild Mountain Thyme" described as.... "Frank McPeak's reworking of Robert Tannahill's ' Brae's O' Balquidder' "