“Coal tonstein of Seam No. 365 (15th Petřvald Coal, Gabriela) of the Upper Silesian Basin. Interesting is root clay at the uppermost part of the sample, indicating coal-vegetation growth directly after the ashfall. U-Pb isotopic age of zircons from this tonstein yielded age 325.64 Ma - Upper Carboniferous age, Serpukhovian stage. Collection of Geological pavilon of prof. F. Pošepný at VŠB-Technical University of Ostrava. ”