Abstract: The Ordovician around the Bosphorus which occupied a large area is composed mainly coarse clasticsediments named Arkose Series no fossil zones have beet found in these series. Near Çengelköy, in a chamositic bedintercolated with a laminated shales, the Middle Ordovician Conulariid Zone has been found (Arıç, 1955; Sayar (Arıç),1970); above these beds ConoeMtina sp. an upper Ordovician CMtinozoan has been identified (Taugourdeau-Abdtisselâmoğlu, 1962). The graywackes which succeeded comformably the laminated shales are probably of Ldandoverian age.About 40 km south-east of Çengelköy the graywackes overlie the Arkose Series and massive quartzite containLower Llandoverian (Rhuddanian) brachiopods in the Eopleetodotonta dupIicata-Cryptothyrella (Hindeîîa) Zonewhere they are associated with the other brachiopods and corals mainly Halysitids. The lower part of the graywackeshave some brachiopods (Skeuidioides aff. asteroidea) associated Diplograptidae (Climacograptus aff. normalis). TheBarchiopod-Graptolitid Zone and its assemblages which have been found the first time in the shelly facies of the LowerPaleozoic Series of Istanbul might be the Uppermost Ordovician-Barly Llandoverian (Kliuddaman At) in age, becausethe typical Ashgillian faunas are not known yet in the Bosphorus area.