Page:Popular Science Monthly Volume 20.djvu/64

54 the year 79. If we include only habitual vents of considerable importance, which we have reason to believe may still be in active condition, the number may be put at between three hundred and three hundred and fifty. Most of these are marked by more or less considerable mountains formed of the matters ejected from them. If we include the mountains which exhibit the main features of volcanoes, but concerning the activity of which we have no record or tradition, the number will not fall much short of one thousand. Then there are other "ruined volcanoes," the cones of which have been worn away and of which the "ground-plans" only are left, still more numerous. The smaller temporary openings, usually subordinate to the habitual vents, known to ancient and modern history and tradition, may be counted by thousands and tens of thousands. The still feebler manifestations—steam-jets, geysers, thermal and mineral waters, fumaroles, mud-volcanoes, and the like—must be numbered by millions. The latter class seem to play a small part as we contemplate them singly, but their force in the aggregate probably far exceeds that of all the great habitual vents. These volcanoes, in all their classes, are very unequally distributed over the globe. Vesuvius is the only habitual vent on the Continent of Europe, and it is on the shores of the Mediterranean; the Mediterranean islands contain six; Africa has ten—four on the western, six on the eastern coast; Asia, so far as is known, twenty-four, twelve of which are on the peninsula of Kamtchatka. None are known in Australia. North America has twenty volcanoes, Central America twenty-five, and South America thirty-seven. In all, one hundred and seventeen volcanoes are situated on the great continental lands, leaving nearly twice that number distributed over the islands of the oceans.

In nearly all cases, the volcanoes are either close to the shores of the continent or at no very great distance from them. The only known exceptions are in the Central Asian plateau and Chinese Mantchooria, concerning which more accurate information is needed. All the oceanic islands that are not coral reefs are of volcanic origin, and many of them contain active volcanoes. A ridge running through the midst of the Atlantic Ocean and embracing the Islands of Jan Mayen, Iceland, the Azores, Canaries, and West Indies, contains forty active volcanoes and a greater number of extinct ones. A similar line in the Pacific Ocean, including the group of islands southeast of the Asiatic Continent, "the grandest focus of volcanic activity on the globe," contains no less than one hundred and fifty active volcanoes; and, if we include those on lines branching from the main one, half the habitually active vents of the globe. A third series of volcanoes starts from near the last one in the neighborhood of Behring Strait, and stretches along the whole western coast of the American Continent, with about eighty active vents.

The volcanoes of the globe thus usually assume a linear