The excursion guidebook describes in an introduction the Brabant Massif and the Condroz Inlier in its tectonic and palaeogeographic context during the Cambrian to Lower Devonian. The excursion describes the main Lower Palaeozoic lithostratigraphic units, their sedimentology, fossil content and structures present in the Brabant Massif, in a north-south transsect using two parallel valleys: the Dyle-Thyle valleys (Cambrian and Ordovician) and the Orneau valley (Ordovician and Silurian). Contrasting lithostratigraphic units, sedimentology, fossil content and structures are shown in the Condroz Inlier, in its western extremity, where two structural units are present: the cen­tral Condroz part and the Puagne Inlier. A new relative dating and a local biozonation, both with chitinozoans, are presented of (parts of) the Corroy, Fumal and Vichenet formations in the Brabant Massif and of the Vitrival-Bruyère, Fosses, Génicot formations and the base of the Criptia Group in the Condroz Inlier. Sedimentological and biostrati-graphical arguments are proposed that may indicate that the Génicot Formation was deposited just before, during and just after the Hirnantian (latest Ordovician) glaciation. This means the first indication of the presence of the latter in Belgium.