At first Donald was half tempted to give the other a scare by firing his own gun close to the slumbering sentry’s ear; but on second thought he decided not to do this. Billie meant well, and was so good-natured; besides, it was hard for any one to get provoked at the fat chum, no matter what happened; because he was always trying to do his level best. Then again, the report would give Adrian a shock, which must seem cruel and unnecessary. Morning found them much refreshed, and ready to take up the new duties of the day. Although Billie had now been quite some time in this country of the Southwest, he had as yet never had but one experience in crossing a desert, and nothing had happened at that time to strike him as odd. Donald warned him that perhaps he was going to experience something now he would not be apt to soon forget. “For they told me,” he went on to add, “at the mine, that this same strip of burning sand lying short of the Zuni village is a particularly wicked place to be caught out on, should one of those sand storms come along.” “Sand storms, did you say, Donald? Now what under the sun can you mean by that? Does it rain sand out here?” Billie wanted to know immediately. “You’ll think it does before long, if we’re so unlucky as to run across such a thing,” Donald told him. “You see,” Adrian explained, “the sand is so fine that when the wind increases to a gale, instead of rain, the air is filled with clouds of sand that choke you, and cause those hills and windrows to come and go, changing after each storm. Over in Africa the Arabs fear them worse than anything else going. They have animals in the camels that are fitted best of all to live through such a storm; and so they just give up, and hide their heads until it’s all over; then dig a way out, and continue their journey.” “Whew! that sounds interesting like,” commented Billie; “and do you think we’ll strike it as bad as that?” “Nobody can say,” continued Donald; “but let’s hope by all means that we get across without any experience of the kind. Perhaps you think it sounds interesting, but take my word for it, Billie, if it comes, you’ll sure believe you’re having the worst time of your whole life.” After that Billie did not seem quite so anxious to know what a sand storm was like. He realized that when his chums took a thing so seriously there must be something about it that was menacing. Donald was right when he said that they had camped not a great ways from where the mountains came to an end, and the glistening desert lay beyond; for two hours after leaving the spring they found themselves on the border of the wide sandy stretch. Billie looked out over that sizzling desert, and began to realize the meaning of what Donald and Adrian had said when they told him about its terrors. But there was no other trail by means of which they could reach the Zuni village; and unless they wished to give that project up for good and all, they must proceed, come what would.