Published online by Cambridge University Press: 01 May 2009
The distribution of Gotlandian volcanic rocks covers a narrow belt running about N. 82° W.–S. 82° E., from South-west Ireland to Bohemia. The rocks comprise rhyolites, andesites, “keratophyres,” diabases, and basalts. Their age varies from early Valentian (Brabant) to Upper Salopian (Bohemia).
The Gotlandian vulcanicity, as a whole, was independent of the preceding Taconic orogeny, neither is its distribution parallel to the main Caledonian folding. The Irish-Belgian section of the belt corresponds closely to the northern boundary of the Westphalian Zone of the Variscan folding, a structural line of fundamental character. The Anglo-Irish occurrences are related to the intersection of this line with Caledonian and Malvernian structures ; those of Belgium and Bohemia are more truly geosynclinal in character.