Silurian and basal Devonian strata can be followed throughout the study area. In the western part the following formations are recognized, in ascending order: Sources (new name) lithographic limestone (which is similar to the White Head Formation), Val Brillant orthoquartzite, Sayabec limestone, St. Leon siltstone (including the Lefrancois Member [new name] which forms a reef complex), and Cap Bon Ami Formation. This sequence is very similar in age and lithology to the one in the Matapedia Valley area. In the eastern part of the area the succession is: Griffon Cove River Formation composed predominantly of heterogeneous terrigenous strata, Sayabec limestone, Roncelles very calcareous mudstone, St. Leon siltstone, and Cap Bon Ami Formation. The Sayabec limestone forms a co venient datum, and both it and the St. Leon Formation are continuous throughout the area. The Roncelles Formation interfingers with the lower half of the St. Leon Formation in the central part of the area. The following formations are dated with fossils: in the west, Sources (late Llandoverian) and basal St. Leon (early Ludlovian); in the east, Griffon Cove River (Pridolian), Sayabec (Pridolian and Gedinnian), and Roncelles (two separate faunas of early and late Gedinnian). A major transgression from the western to the eastern part of the area occurred in Pridolian time. The following formations are time transgressive, and are youngest at their eastern outcrop: Sayabec (Wenlockian-Gedinnian), St. Leon (Ludlovian-Gedinnian), and Cap Bon Ami (Pridolian-Siegenian). The position of the Silur an-Devonian boundary in Gaspe Peninsula is discussed in relation with the position of this boundary in the so-called "standard" (of New York) for the Devonian of North America.