K.M. Towe T. G. Gibson 1971 A series of closely time-equivalent deposits that correlate with seismic reflector horizon A exists along the coast of eastern North America. These sediments of Late-Early to Early-Middle Eocene age contain an authigenic mineral suite indicative of the alteration of volcanic glass. A volcanic origin for these siliceous deposits onshore is consistent with a volcanic origin for the cherts of horizon A offshore. application/pdf 10.1126/science.172.3979.152 en American Association for the Advancement of Science Eocene volcanism and the origin of horizon A article