"From 425 to 500 million years ago" . . . . "International union of geological sciences. International Subcommission on Ordovician Stratigraphy." . . . . . "Ordovician System of Tuva (Southeastern Russia)" . . . . . . . . . . . "The Ordovician system of the East European Platform and Tuva (southeastern Russia) correlation charts and explanatory notes"@en . . . . . . . . . . "Ordovician System of the East European Platform (Estonia, Latvia, Lithuania, Byelorussia, parts of Russia, the Ukraine and Moldova)" . "The Ordovician system of the East European Platform and Tuva (southeastern Russia) : correlation charts and explanatory notes" . . . "The Ordovician System of the East European Platform and Tuva Southeastern Russia : correlation charts and explanatory notes" . . . .