From "The Wonders of Ireland" by P. W. Joyce, 1911
Among the wonders of this country, the old writers include the sudden disappearance of two lakes. One of these, called Lough Lee (the lake of the calf), was situated in Burrishoole near the shore of Clew Bay in Mayo. The following are the words in which the event is recorded in the Book of Ballymote:--"Lough Lee in the territory of Umallia (i.e. Burrishoole) ran off into the sea, so that nothing remained of it but its place." According to the Four Masters, who notice the same event, it occurred in the year of our Lord 848.
Another lake, called the lake of Seeoran, in the mountains of Slieve Gorey in the County Cavan, flowed away suddenly, its water running into a river called Favall. This event happened, according to the Four Masters, towards the end of the night of the festival of St. Michael, A.D. 1054. The next morning when the people looked out the lake was gone, and the Four Masters add, what we may well believe, that the occurrence caused great amazement throughout the whole neighbourhood.
Seeoran is the name of a townland about four miles north-west from Bailieboro' in Cavan, but there is now no lake, and the people have quite lost the tradition of its former existence and disappearance. The little river that flows southward through Virginia into Lough Ramor is probably the stream anciently known by the name of Favall; but this name is also forgotten.*
* Occurrences like those recorded here, though very rare and very extraordinary, are not wonders as we commonly understand the word; for they are due to natural causes. We know that lakes sometimes disappear very suddenly, especially after earthquakes, owing to the formation of underground clefts or passages which carry off the water.