Of volcanic origin , the islands of Saint Helena , Ascension Island , and Tristan da Cunha were all formerly separate colonies of the English crown , though separately discovered by several Portuguese explorers between 1502 and 1504 .
Of volcanic origin , the islands of Saint Helena , Ascension and Tristan da Cunha were all formerly separate colonies of the English crown , though separately discovered by several Portuguese explorers between 1502 and 1504 .