The cave that held fast the bones of these ancients lay somewhere in the bewildering maze of cañons across the valley. Bill Jonathan would recognize the spot, so he had declared whenever Abington questioned him. A certain rock on the cañon’s northern rim, shaped like the head of a huge rhinoceros with two tusks on his snout—Bill was positive he could not miss it, once he got inside the cañon. The opening to the cave was directly under the first tusklike rock spire. A matter of ten miles perhaps, Bill had guessed as he stood on the ledge and gazed across.

Here on this side were caves and even with the hope of finding the fossil skeletons Bill had described, Abington had wanted to explore these before going on. He still wanted to do so, if he and Bill could manage to hunt down the unknown pillager of camps, or at least guard their supplies against further depredations. If the raid on Bill’s cave had been as complete as on his own camp, he would be compelled to postpone all research work while he plodded with the burros to the nearest town for fresh supplies. Bill could not go, that was certain.

At daybreak Abington was planning drowsily to send Bill up the cañon after the burros, load on what was left of the outfit and cross immediately to the other side of the valley, where they would endeavor to find the skeletons first of all and be sure of them before he went out for supplies. He would then be able to take out specimens to send on to his museum, thus saving a bothersome trip later on.

His hand reached out to shake Bill’s leg and rouse him to the day’s work, when a great clattering sounded in the cañon mouth near by. Bill needed no shaking to bring him to his feet. As the two automatically faced toward the noise, there came the three burros in a panicky gallop out of the cañon and into the open.

In one great leap Bill left the ledge and ran yelling and flailing his arms to head them off before they stampeded down the valley. The leading burro, a staid, mouse-colored little beast, swerved from him, wheeled toward the hills opposite, stumbled and fell in a heap. The second kept straight on down the valley, the third burro at its heels. Bill let them go while he ran to the fallen leader.

Though it took but a minute to cover the short distance, the burro’s eyes were already glazing when Bill arrived. As he stopped and bent over it a shuddering convulsion seized its legs and immediately it stiffened. It was dead.

Bill stood dumfounded, eying it stupidly for a moment before he turned to call Abington. But the shout died in his throat, for his glance had fallen upon a fresh disaster. The two other burros were down and kicking convulsively, just as the first had done. They were dead before he could reach them.

Abington was not in sight when Bill, walking heavily under the burden of this new tragedy, returned to the ledge; but presently he came limping out of the cañon and into camp.

“I thought I could discover what had stampeded the burros,” Abington said, coming up with an indefinable air of surprise that Bill should be standing there passive with that blank look on his face. “Too late, again. If it was the gosh-awful, he’d disappeared before I could get up there. Did you head off the burros? I want to move camp this morning.”