The Tertiary included times of widespread and intense volcanic action in other continents as well as in North America.  In Europe, Vesuvius and Etna began their career as submarine volcanoes in connection with earth movements which finally lifted Pliocene deposits in Sicily to their present height,—­four thousand feet above the sea.  Volcanoes broke forth in central France and southern Germany, in Hungary and the Carpathians.  Innumerable fissures opened in the crust from the north of Ireland and the western islands of Scotland to the Faroes, Iceland, and even to arctic Greenland; and here great plateaus were built of flows of basalt similar to that of the Columbia River.  In India, at the opening of the Tertiary, there had been an outwelling of basalt, flooding to a depth of thousands of feet two hundred thousand square miles of the northwestern part of the peninsula, and similar inundations of lava occurred where are now the table-lands of Abyssinia.  From the middle Tertiary on, Asia Minor, Arabia, and Persia were the scenes of volcanic action.  In Palestine the rise of the uplands of Judea at the close of the Eocene, and the downfaulting of the Jordan valley were followed by volcanic outbursts.  In comparison with the middle Tertiary, the present is a time of volcanic inactivity and repose.

Erosion of tertiary mountains and plateaus.  The mountains and plateaus built at various times during the Tertiary and at its commencement have been profoundly carved by erosive agents.  The Sierra Nevada Mountains have been dissected on the western slope by such canyons as those of King’s River and the Yosemite.  Six miles of strata have been denuded from parts of the Wasatch Mountains since their rise at the beginning of the era.  From the Colorado plateaus, whose uplift dates from the same time, there have been stripped off ten thousand feet of strata over thousands of square miles, and the colossal canyon of the Colorado has been cut after this great denudation had been mostly accomplished.

On the eastern side of the continent, as we have seen, a broad peneplain had been developed by the close of the Cretaceous.  The remnants of this old erosion surface are now found upwarped to various heights in different portions of its area.  In southern New England it now stands fifteen hundred feet above the sea in western Massachusetts, declining thence southward and eastward to sea level at the coast.  In southwestern Virginia it has been lifted to four thousand feet above the sea.  Manifestly this upwarp occurred since the peneplain was formed; it is later than the Mesozoic, and the vast dissection which the peneplain has suffered since its uplift must belong to the successive cycles of Cenozoic time.

Revived by the uplift, the streams of the area trenched it as deeply as its elevation permitted, and reaching grade, opened up wide valleys and new peneplains in the softer rocks.  The Connecticut valley is Tertiary in age, and in the weak Triassic sandstones has been widened in places to fifteen miles.  Dating from the same time are the valleys of the Hudson, the Susquehanna, the Delaware, the Potomac, and the Shenandoah.