FLETZ, adjective In geology, the fletz formations, so called, consist of rocks which lie immediately over the transition rocks. These formations are so called because the rocks usually appear in beds more nearly horizontal than the transition class. These formations consist of sandstone, limestone, gypsum, calamine, chalk, coal and trap. They contain abundance of petrifactions, both of animal and vegetable origin.
Source: Webster's 1828 American Dictionary ↗ · public-domain · returned verbatim, no AI