concretions - ironstone concretion from Madagascar - hand specimen

Similar lumpy ironstone concretions weather out of sandstone in the Cretaceous Dakota Formation in Ellsworth County, Kansas. The concretions shown here were and are widely sold as fossilized turtle dung from Madagascar.During the Scottish Enlightenment, early geologists began to realize that processes that they observed on the surface of the earth were the same as processes that had operated on the earth's surface in the past. The concept became known as Uniformitarianism and was summarized by James Hutton, the father of geology, as "The present is the key to the past." Sir Charles Lyell popularized the concept in his 1830 Principles of Geology, and it is a guiding principle of geology today. Why mention this? You would be hard pressed to find an animal of any kind that produces a dropping that looks like these concretions, yet sellers, knowingly or unknowingly, present them as fossilized turtle dung. A good opportunity to discuss a basic principle of geology with your students, and to