There are more volcanoes in our country than is generally supposed. Some are very small and some rank among the greatest of mountain peaks, but all together there are many hundreds, perhaps thousands, of them. At present they are all silent and apparently dead. We are accustomed to speak of them as extinct volcanoes, but of this we must not be too sure.
They stand dark and cold, giving no clue to the nature of the forces which made them, except perhaps by the presence of an occasional hot spring and the appearance of the rocks of which they are composed. The slag-like character of these rocks we have learned to associate with intense heat. Some of these volcanoes are very old and have been nearly worn away; others are new and almost as perfect as when they were first made.
Where shall we go to find these volcanoes? Are there any upon the Atlantic coast or neighboring highlands? Though you may travel over all that portion of our country, you will find none, although you will discover in places, as for instance in the palisades of the Hudson, lavas which came from very ancient volcanoes, worn down so long ago that their very sites are lost to view.
If we search the Mississippi basin we find there even fewer traces of volcanic action than upon the eastern highlands. The greater portion of the vast area embraced by the Mississippi River and its tributaries has had a very uneventful history, although at times earthquakes may have occurred and the sky may have been darkened by ashes from eruptions in distant parts of the earth.
FIG. 25.—FISSURE IN THE LAVA, SHADOW MOUNTAIN
The groovings in the lava show that it was squeezed out in a half-solid condition
It is in the country west of the Rockies, the region last to be explored and settled, that the objects of our search come to light. Here are volcanoes and lava fields so extensive as almost to bury from sight the older surface of the earth. Some of them appear as if but yesterday they had been glowing with heat.
In the Cordilleran region Nature has carried on her work with a master hand. She has lifted the earth's crust to form a great plateau. Portions of the plateau she has broken, projecting the fragments upward to form lofty mountains, while along the fissures thus created she has squeezed out fiery molten matter from the interior of the earth. This molten material has spread out in fields of lava or has piled itself about small openings, forming volcanic cones, which in some cases have overtopped the loftiest mountain ranges of the continent. It is believed that a number of these volcanic eruptions have occurred in the Cordilleran region of the United States since the discovery of America, and that one took place within the lifetime of many persons now living.
San Francisco Mountain, in northern Arizona, is the loftiest volcanic peak of a region dotted with volcanoes and lava flows. This great volcano, like most of its neighbors, has long been extinct, although a few miles to the eastward there appears a group of small but very new cones.