THE DARK HILLS AND THE FIGURES IN WHITE
"The Baths of the Damned," the superstitious Arabs call the region of the Northern Sahara in which you come upon these strange white figures. The fearsome name was suggested by the fact that the figures slowly rise from some hot region inside the earth. In reality they are mounds of carbonate of lime deposited by the water of hot springs heavily charged with dissolved limestone. Similar springs in our Yellowstone Park spout up in the form of geysers and form "geyser basins"—huge stone tubs. Here in the desert the water doesn't spout; it bubbles up slowly and so builds the mounds. In the background you see black masses of volcanic rock, for this, like Yellowstone Park, is a volcanic region where the underground rocks haven't cooled off.
A CHAOS OF COLOR IN THE ROCKS
The desert wears rocks and stones of as many colors as the jewels of Oriental kings. It also runs much to solemn black in its heaps of volcanic rock with cold limestones on the heights; but you can see blue-grays, browns, ochres of every shade gleaming in the sun, the reds of the rusting iron in them staining the precipices and the walls; and there are purples and pinks and dark greens and violets. These colored rocks are often fantastically mixed together, like the colors on an Easter egg.
THE SKELETONS OF THE DEAD RIVERS
And here we come upon one of those skeletons of dead rivers that I spoke about. There they are, the river valleys and the river beds, full of sand and gravel, and with boulders along the banks, and branch valleys running into them; a river system all complete but for one thing—water. It's just as if the main valley and the branches had been made all ready but the river never came; or as if there had been rivers there once but they couldn't stand the climate! Of course, when a cloudburst comes along it helps itself to these ready-made river-beds; but for the most part they stand as empty as the ruins on the desert's edge in which
... the lion and the lizard keep
The courts where Jamshyd gloried and drank deep.[30]
[30] "The Rubaiyat" of Omar Khayyam.
Not only do the size of the river-beds show that there used to be more frequent rains in these regions of desolation, but right at the edge of the northern Sahara are the remains of immense aqueducts; great troughs built of stone and carried on bridges from the source of a water supply to a city. When the Romans owned the earth—including the Sahara desert—they were famous builders of these aqueducts.