Ashley, G. H. (1933). The scenery of Pennsylvania: Its origin and development based on recent studies of physiographic and glacial history. Harrisburg, PA: Dept. of Internal Affairs, Topographic and Geologic Survey.

Ashley, George H. The Scenery of Pennsylvania: Its Origin and Development Based On Recent Studies of Physiographic and Glacial History. Harrisburg, PA: Dept. of Internal Affairs, Topographic and Geologic Survey, 1933.

Ashley, George H. The Scenery of Pennsylvania: Its Origin and Development Based On Recent Studies of Physiographic and Glacial History. Harrisburg, PA: Dept. of Internal Affairs, Topographic and Geologic Survey, 1933.