Adam proceeded cautiously behind the burros. They did not like the travel, and, wary little beasts that they were, they stepped gingerly in places, as if trying their weight before trusting it upon the treacherous-looking crust. Adam felt the beat of the sun upon him, and the reflection of heat from the valley floor. He had been less oppressed upon hotter days than this. The sensations he began to have here were similar to those he had experienced in the Salton Sink, where he had gone below sea level. The oppression seemed to be a blood pressure, as if the density of the air closed tighter and heavier around his body. At last the burros halted. Adam looked up from the careful task of placing his feet to see that he had reached a perfectly smooth bed of salt, glistening as if it were powdered ice. This was the margin of the place that from afar had looked like a frozen stream. Stepping down upon it, Adam found that it trembled and heaved with his weight, but upheld him. There was absolutely no sign to tell whether the next yard of surface would hold him or not. Still, from what he had gone over he believed he could trust the rest. As he turned to retrace his steps he saw his tracks just as plainly in the salt as if they had been imprinted in snow. He led Jennie out, and found that, though her hoofs sank a little, she could make it by stepping quickly. She understood as well as he, and when released went on of her own accord, anxious to get the serious job over. Adam had to drive the other burro. The substance grew softer as Adam progressed, and in the middle of that glistening stream it became wet and sticky. The burros labored through this lowest level of the valley, which fortunately was narrow. On the other side of it extended a wide flat of salt and mud, very rough, upheaved as if it had boiled and baked to a crust, then cracked and sunk in places. Full of holes and pitfalls, and rising in hummocks gnarled and whorled like huge sea shells, it was an exceedingly toilsome and dangerous place to travel. The crust continually crumpled under the hoofs of the burros, and gave forth hollow sounds, as if a bottomless cavern ran under the valley floor. As Adam neared the other side he encountered thin streams of water that resembled acid. It was necessary to find narrow places in these and leap across. Beyond these ruts in the crust began an almost imperceptible rise of the valley floor, which in the course of a couple of miles led out of the broken, choppy sea of salt to a sand-and-gravel level. How relieved Adam was to reach that! He had been more concerned for the safety of the burros than for his own.