Dictionary of Ichthyology  

toadstone = fossil fish teeth used in the Scottish Highlands as a folk medicine to arrest bleeding, and elsewhere as an antidote to poison and for treatment of leprosy. They were thought to be found in or produced supernaturally by toads. Toadstones may be teeth from Lepidotes, an extinct ray-finned fish from the Jurassic and Cretaceous periods.

Extraction and use of a toadstone from a 1497 illustration by Johannes de Cuba, Wikimedia Commons: http://en.wikipedia.org/wiki/File:Extraction_d%27une_crapaudine.jpg

Canadian Museum of Nature