Description:A photograph of rock formations known as "Pillow Lavas". There is a hammer in the photograph to indicate scale. The caption at the back of the photograph reads "Pillow Lavas' erupted on an early Ordovician seafloor about 500 million years ago provide evidence of an ancient seaway, the Iapetus Ocean, which separated the northern and southern parts of Ireland. The ocean may have been 4000 Km. wide and was floored by basalt, a basic igneous rock.".