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most of Arizona the river phenomenon is enlarged to the scale of lakes, some of them of large dimensions, while bored wells give artesian flows similar in character to those developed east of the Rockies.
The water-supply of these beds all comes from the mountains. The great distributer to the most of them is the chain of the Rockies. These mountains, like the other important ranges in the West, have risen, and their high peaks are Archaean. The rock formation lying lowest pushed up, bulging the various outer layers of the earth’s skin, until finally it has broken through and gone far out above them. A great fracture has been made in the earth’s crust, and a long wedge of the interior substance has risen out of the depths and ascended high in the cold sky and hardened there. The lips of this wound, on both sides of the central tongue, expose the foliated character of the earth’s structure. The strata have been broken and left standing flexed abruptly upward against the sides of the tongue. Often the topmost strata have slid down the synclinal curve or basin thus made, and then the bent edges stand a little distance away from the mountains and form foot-hills. The intervening declivity between the upturned edges of the beds and the base of the Archaean tongue are filled in with débris, the result of degradation of the rocks on both sides of the chasm.
From this, therefore, it can be seen that these saturated sandstones have their edges directly in the regions where lie the great reservoirs of congealed water, the mountain snows. Sometimes the snows cover the edges of the strata; at other places the water drains from the frozen zone down the high granites until it strikes the sandstones, and is then absorbed, sucked up, and drawn off. When these stones are filled, as I have said, the water will run over their edges and find its way into the streams to be carried off.
The lowest member of pervious sandstone must, of course, lie upon some impervious rock. But intercalated between this and the porous stratum above are impermeable beds, generally of clay, and above the porous rock there are similar beds. These non-saturable strata perform a highly important office in the scheme of phreatic flows. From the sides of the mountains the strata dip toward the valleys, so that for long distances the water moves upon a grade much lower than its head. If the entire series of strata, from the surface down to the metamorphic rocks, were pervious, the water would run upon the plane nearest to the level of its head, and, unless the flow were lessened or stanched, it would not sink into the rock beneath. Under such an arrangement the great purpose of nature in holding water in the arid region would be defeated, for the water would quickly rush from the mountains to the sea, and would all be lost.
But the dense and occluded beds superimpose the loose and granular ones; and, thus held down and imprisoned: the water is transported hundreds of miles from its mountain source. When these clay or shale beds are punctured by the drill, and the fat, water-reeking rock beneath is touched, the water will rise in the bore to a height level with its source; and, as the arable lands generally lie in the valleys upon a plane lower than this, the liberated waters will, under hydrostatic pressure, shoot up in a column above the surface of the land. This is
