The footwall unit below the Mesozoic nappe complex of the Humenske vrchy Mts. has been reached by the MLS-1 Podskalka borehole. The lowermost (1769–1833 m) sandstone/claystone formation in this borehole it is constrained to be Late Cretaceous? but rather Paleogene in age (according to the youngest nannofossils). The hangingwall of these sediments consists of the Krizna Nappe complex which comprises formations from Middle Triassic up to Albian in age. The observations from the MLS-1 borehole point to the underthrusting of the externally seated flysch units beneath the collisional edge of the Centrocarpathian plate. The Paleogene formations may be attributed to the same unit which being deeply underplated, buried, and than exhumed in the East Slovak Basin floor (Inacovce-Krichevo Unit). The Paleogene formations of this unit suffered sub-greenschist metamorphism and they are overlapped by ultrabasic thrust slices (Zbudza-1 borehole).