Available K-Ar dates from the Palisades sill (142 to 202 m.y.) are generally younger than the ages of post-Triassic intrusive rocks in other areas. 40Ar/39Ar release spectra of chill-zone samples record ages of 192 and 186 m.y. and furnish no evidence of postcrystallization argon loss. These ages are similar to published K-Ar biotite ages (186 to 196 m.y.) and probably refer to the time of crystallization of the sill. As recent paly-nologic studies in the Hartford basin have shown that rocks stratigraphically equivalent to those intruded by the Palisades are, in part, of Early Jurassic age, the 40Ar/39Ar ages are not inconsistent with absolute age brackets on the Triassic Period.

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