Webster's 1828 Dictionary
FLETZ
a.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.
Duden Dictionary
Fletz
Fletz Substantiv, Neutrum oder Substantiv, maskulin süddeutsch , das oder der |Fl e tz auch flɛt͜s |das oder der Fletz; Genitiv: des Fletzes, Plural: die Fletze mittelhochdeutsch vletze, Flöz Hausflur