Abstract

Old Red Sandstone deposits of the Caledonian intermontane basins extended far beyond the present outcrop limits and a large paralic basin or transition zone between the highlands and the Theic Ocean existed between Early and Late Devonian times. Extrapolating from general models and from outcrop areas of the Acadian Old Red Sandstone, it is tentatively suggested that the Acadian orogeny produced and involved similar basins, extending and rejuvenating continental deposition beyond the Caledonide belt. Relatively little of the resulting sediment is known in outcrop east of the Acadian-Appalachian highlands, but extensive bodies of red beds or other continental strata may underlie the continental shelves of western Europe and north-eastern North America. Other similar deposits may have formed on the western side of the Caledonian Orogen.

While the upland areas were probably almost devoid of vegetation, the transitional zone supported a widespread and locally abundant (equatorial) flora. The Caledonian continental collision allowed the mingling of the previously rather distinct European and American vertebrate faunas and the Acadian collision provided the opportunity for the vertebrates of ‘North Atlantis’ to spread immediately into Gondwanaland.