It is the opinion of Dana that while there have been volcanoes during the different geological ages, yet volcanic activity has increased through the geological past until the age that immediately preceded the appearance of man on the earth. He thinks there is no reason for believing that there were any very great volcanic eruptions during the earliest geological time known as the Archæic. Dana speaks as follows concerning this: "In this connection it is an instructive fact that in eastern North America, at epochs when there was the greatest amount of friction and crushing ... those of the making of the Green Mountains and the Appalachians ... no volcanoes were made, and little took place in the way of eruptions through fissures." On the other hand, Prestwich seems inclined to think that the absence of well-marked cones of volcanic material in the rock of the older geological ages is not to be regarded as proof that no eruptions then took place, since the very great amount of erosion that occurred between that time and the Tertiary Age before the appearance of man, would, probably, have completely obliterated any cones, and even the volcanic materials would have undergone such changes as completely to alter their general character. He agrees, however, with Dana that, probably, the most violent and explosive volcanoes of the geological ages have been those of the Tertiary Age. Without, however, attempting anything more than a brief reference to the volcanoes of the geological past, it may be said that many of the more important of the active volcanoes of the earth's present time were begun in the Tertiary Age. Mt. Etna, Vesuvius, and Mt. Hecla are believed to have commenced at this time. There is an interesting region of geological volcanoes in the neighborhood of Auvergne in Central France. Here they occur in three separate groups that extend over a high granite platform from north to south for a distance of about 100 miles, and from twenty to eighty miles from east to west. The eruptions began in the earlier portions of the Tertiary Age, and continued down to the latter periods of prehistoric times. Some of these volcanic craters remain to-day almost as unaffected by erosion as if they had been formed but recently. Other regions of geological volcanoes are to be found in parts of Spain near the foot of the Pyrenees Mountains, in parts of Italy and Germany, as well as in regions in the Caucasus Mountains. In Asia Minor there exists a group of almost thirty extinct volcanoes in the neighborhood of the Gulf of Smyrna. Both Little and Great Ararat contain volcanic cones: that in the latter mountain was active during historical times. There are also extensive volcanic districts in the Taurus Mountains. In addition to these there are groups of extinct volcanoes in portions of Central Asia.