'Purgatory', 1872. Cliffs on the Atlantic coast of Rhode Island, USA: 'precipitous rocks, with the deep and sharp-lined fissure... The opening in the cliff extends one hundred and sixty feet, and is fifty feet deep at the outer edge. It is from eight to fourteen feet wide at the top, and from two to twenty at the bottom. It was once supposed that the water at the base was unfathomable; but at low tide it is actually not more than ten feet in depth. It was formerly the prevailing theory that this fissure was occasioned by a sudden upheaving of the rock; but, after careful examination, Professor Silliman came to the opinion that it was probably formed by the gradual eating away of the softer portions of the stone at a very early period'. From "Picturesque America; or, The Land We Live In, A Delineation by Pen and Pencil of the Mountains, Rivers, Lakes...with Illustrations on Steel and Wood by Eminent American Artists" Vol. I, edited by William Cullen Bryant. [D. Appleton and Company, New York, 1872]