I got this story from Michael Gillespie. He lives in Ballymacarter. He told me that his uncle told him about a giant who lived in Magilligan. He was a strong man. He was twelve foot high. He and another man were quarrying stones. This giant could lift a stone over a ton in weight. They came on a stone which was long and flat. They found some treasure under the stone. Away they went and got drunk. They began to fight about which of them could lift the stone. The giant said he would throw it to the other side of the water. He did so and it is there in Ballybrack since.
From the Schools Collection made in the 1930s, and now being digitised at duchas.ie. There is another story about the stone here...
There is a "standing stone" in Ballybrack. People of the neighbourhood say that this stone was thrown from Magilligan by a giant before he had got his breakfast. Other people say that a great warrior is buried there and that the stone was put there to mark the grave.
Stands upright out of the ground by the roadside at Ballybrack, Moville. About 4 1/2 feet high and 4 yards from the roadside. There are marks on it, some people say it is ancient writing.
Finn McCool is said to have thrown it from the other side of Lough. Another version or legend says it marks the grave of a Dane, for Danes occupied L. Foyle in their day.
It is also said that two giants were fighting, one on either side of L. Foyle, and that this stone was thrown from the Derry side and struck the Giant in the head and crushed him into the ground here.