The presented research deals with sedimentological analysis of black thin- to medium-bedded limestone that forms the uppermost part of the Idrija mine structure. The formation was logged in two sections: the first section is located above the Idrija cemetery (Skrnik), while the second section lies close to the Rake promenade. From the collected samples, thin sections were made to determine the microfacies association. Conodont analysis was made for age determination. The succession consists mainly of thin- to medium-bedded micritic limestone, which is locally parallel and cross-laminated. Micritic limestone includes several microfacies types: laminated mudstone with rare radiolarians, radiolarian-fillament wackstone and filament-peloid packstone. Intercalated between micritic limestone are medium-bedded calcarenites with mollusks and limestone breccia. These two facies types include the following microfacies types: poorly washed packstone, floatstone with peloid-rich matrix and intraclastic-mollusc floatstone-rudstone. Facies association points to sedimentation on the slope or at the foot of the slope in a deep-sea basin. Hemipelagic sedimentatiton was interrupted by distal calciturbidites and debris flows. They both transported shallow-water material into the basinal environment. The finding of a conodont species Pseudofurnishius murcianus Van den Boogaard suggests upper Ladinian age of the formation.