Page:Popular Science Monthly Volume 32.djvu/842

838 received the generic name of geyser, from the Icelandic word signifying to spout. One of the most remarkable geyser regions in the world is in the western part of the United States, near the borders of Wyoming Territory, where are grouped together more than two thousand very hot springs, which we might imagine to have been engendered by some vast steam-furnace.

Waters may also acquire a high temperature by borrowing from eruptive rocks which have been thrown up from greater depths and still retain a part of their primitive heat. They generally rise by the force of hydrostatic pressure, as in the artesian wells, while the expansive force of vapor is sometimes the elevating agent. Volcanoes, the eruptions of which suggest only the idea of fire, constitute, in fact, gigantic intermittent springs of water, the temperature of which surpasses everything that we can comprehend.

Thus, the vapor of water not only forms the most abundant and most constant product of eruptions, but it seems even to be, through its enormous tension, the mother of them. From the very beginning of the crisis it bursts out in enormous spurts, dragging matter of every kind up the subterranean conduit. This vapor produces a vertical column which spreads out in the upper regions of the atmosphere in the shape which in Italy Pliny has compared to that of a pine-tree. It is sometimes blackened, especially at the beginning of an eruption, by solid dejections of cinders or lapilli. The watery column may reach a considerable height if it is not carried away or dissolved by aerial currents. Torrential rains frequently fall from the clouds engendered by these exhalations.

Impossible as it may appear, water is incorporated in fused and incandescent lavas, and consequently participates in a temperature exceeding 1,000°; but when it is vaporized its temperature falls at once to the boiling-point.

The water expelled from volcanoes gives only a very limited idea of the importance of the domain of that fluid in the depths of the earth. When we consider how many opportunities it finds to penetrate by capillarity and other means into interior regions of a very high temperature, we can not doubt that these regions contain superheated water. Imprisoned within rocky walls that offer an enormous resistance, it acquires a tension which recent experiments show to be of marvelous power.

Water also contributes invisibly to mechanical actions. In view of the immense force it exhibits in eruptions, we have a right to suppose that in regions where it has no outlet it may, under the force of its enormous pressure, be also an effective cause of the most formidable earthquakes, which are simply volcanic eruptions without outlet. These agitations are produced more especially in countries the ground of which is dislocated and has most recently acquired its present relief. Such a geological constitution, which is recognized as