Fig. 691.—Distribution of land and water.
Water has enormous power of disintegration. We have only to cast our eyes upon the illustrations in any volume of continental travel in Europe or America to perceive the gorges and cañons worn out by the resistless and frequently gently-flowing river to estimate the part which water plays in Physical Geography and Meteorology.
But springs occur not only in the case mentioned; there are mineral springs, hot springs, and oil springs, all following the same rules of nature. The Artesian well has been mentioned. The Geysers of Iceland have often been portrayed, and are amongst the most wonderful phenomena of nature. These will serve as a type of the other thermal springs, of which the districts of the Yellowstone in North America afford perhaps the most extraordinary instances. These are intermittent springs, and the water rises to a great height, at intervals of about an hour and a half; and after many successive attempts, or trials, as it were, the geyser shoots up to a great height enveloped in steam.
The cause of these well-known phenomena have been explained by Bunsen, and it has already been referred to. We know that at a certain air-pressure water boils at 212° (Fahr.), but on mountains at less pressure it will boil before that degree, because the air is rarefied. So conversely, under the ground, it may reach 212° without boiling. So the surface (warm) water falls, and reaches a high temperature before it is converted into steam. When it is so converted, the vapour is formed very rapidly, and the expansive force is tremendous, shooting up the water and all the contents of the tube with terrific violence, and with a beautiful effect. Pressure therefore alters the boiling point of water.
Fig. 692.—Geyser of the Yellowstone.
The mineral springs of Bath and many continental towns owe their properties to the solvent power of water, which assimilates the mineral atoms and gases. They arise just in the same way as the ordinary spring, the taste and smell depending upon the soil and strata. Perhaps the oil wells are the most curious phenomena of this kind. They are excavated upon the Artesian principle. The petroleum is bored for, as we bore for water, and the oil rushes up with great force, and in enormous quantities. Gas wells are also to be found in Pennsylvania, and have supplied towns with gas for years. Both these Artesian wells are caused by the decay of vegetation. The gas is in the coal formation, and the oil has been pressed out from vegetable deposit, and as anthracite is a stony coal, petroleum is a kind of coal-tar, of natural formation.
Fig. 693.—Colorado Cañon (effects of water erosion).
We have alluded to the river, which emerges from the spring, which has fallen as rain. But there is another, and, to many minds, a much more interesting form of the universal fluid we call water. This is ice. Familiar as ice is, either to the stay-at-home invalid, the skater, and the traveller, there is a great deal to be said about it. It is a subject we would dwell upon had we space, for the remembrance of many a pleasant hour passed upon snow and glacier call upon us to go back again, even though only in imagination. No one who has not climbed the glacier—even the Mer de Glace to the Jardin, now such a common excursion—can fail to be struck with the beauty and grandeur of the scene presented to him, and to carry away a fond recollection of the icy regions he penetrated.