Oases in the waste.
In every desert there are isolated places where water stands in pools, fed by underground springs, where mesquite and palms grow, and where there is a show of coarse grass over some acres. These are the so-called oases in the waste that travellers have pictured as Gardens of Paradise, and poets have used for centuries as illustrations of happiness surrounded by despair. To tell the truth they are wretched little mud-holes; and yet because of their few trees and their pockets of yellow brackish water they have an appearance of unreality. They are strange because bright-green foliage and moisture of any kind seem out of place on the desert.
Catch-basins.
Old sea-beds.
Yet surely there was plenty of water here at one time. Everywhere you meet with the dry lake-bed—its flat surface devoid of life and often glimmering white with salt. These beds are no doubt of recent origin geologically, and were never more than the catch-basins of surface water; but long before ever they were brought forth the whole area of the desert was under the sea. To-day one may find on the high table-lands sea-shells in abundance. The petrified clams are precisely like the live clams that one picks up on the western coast of Mexico. The corals, barnacles, dried sponge forms, and cellular rocks do not differ from those in the Gulf of California. The change from sea to shore, and from shore to table-land and mountain, no doubt took place very slowly. Just how many centuries ago who shall say? Geologists may guess and laymen may doubt, but the Keeper of the Seals says nothing.
Volcanic action.
Lava streams.
Nor is it known just when the porphyry mountains were roasted to a dark wine-red, and the foot-hills burnt to a terra-cotta orange. Fire has been at work here as well as wind and water. The whole country has a burnt and scorched look proceeding from something more fiery than sunlight. Volcanoes have left their traces everywhere. You can still see the streams of lava that have chilled as they ran. The blackened cones with their craters exist; and about them, for many miles, there are great lakes and streams of reddish-black lava, frozen in swirls and pools, cracked like glass, broken into blocks like a ruined pavement. Wherever you go on the desert you meet with chips and breaks of lava, showing that at one time there must have been quantities of it belched out of the volcanoes.
Geological ages.
Kinds of rock.