From "The Wonders of Ireland" by P. W. Joyce, 1911
On the 16th of March, the eve of the festival of St. Patrick, in the year 804, there happened a great storm of thunder, lightning, and wind, which exceeded so much in violence all the storms ever before witnessed, and so terrified the people, that it was recorded among Ireland's Wonders, It raged chiefly in the county Clare; one thousand and ten persons perished in the old territory of Corcobaskin alone, in the west of the county; and when the people of the coast looked out on the morning of St. Patrick's Day, they found, as part of the fearful work of the night, the island of Inis-fithi divided into three parts.
Inis-fithi is the well-known island now called Inish-Keeragh ("Sheep Island") or Mutton Island, near Miltown Malbay; and the portions severed from the main body are the two masses of rock which rise out of the waves immediately north of the island.
It will be observed that this wonder is a natural occurrence. Moreover it is historical, as it is recorded in all the principal annals, such as those of Ulster, of Clonmacnoise, and the Four Masters; and although it is eleven centuries since it happened, a vivid tradition of the catastrophe is current to this day among the people of the west of Clare.