The Carboniferous Period In North America was, on the whole, a time of tranquillity, with oscillations of level and shifting of the boundaries of land and sea from time to time, such as have been described in the foregoing pages. A very general upheaval of the continent brought the Mississippian to a close and the succeeding time of erosion was followed by some folding in the Appalachian region, the formation of the Pottsville trough and the renewed transgression of the sea. Volcanic action appears to have been confined to the Pacific coast region; the Lower Carboniferous of British Columbia is largely made up of volcanic material, and vulcanism was manifested in the Upper Carboniferous of the coast from Alaska to California. In northwestern Kentucky and southern Illinois the Carboniferous rocks are cut by dykes, but these may have been formed at a long-subsequent time.