The chronology of the Taconic orogeny is variously documented and can only be revealed through a careful consideration of all the chronologically pertinent evidence. The Late Ordovician post-metamorphic cooling event (uplift) revealed by K–Ar analysis of the Green Mountain schists was initiated 440 m.y. ago. Field evidence—the pre-Caradoc (445 m.y.) unconformity and the commencement of deposition of argillaceous sediments of Caradoc age—confirms this interpretation of the isotopic data.