This was little past mid-afternoon. They had left the sahuaros behind and were coming down among widely scattered salt bushes to the border of an utterly barren alkali flat. For the first time since the stop in the mesquite, Carmena halted her quick advance. But it was not to rest. The feverish crimson of Lennon's face sobered her reassuring smile. She peered searchingly back along the trail, glanced at the sun, and hastily transferred to their empty canteens all but a quart from the full canteen on the saddlehorn. "We've got to make it last till sundown, Jack," she warned. "Then, if only we can hold our lead, we'll be able to keep going all night." Lennon drew out two half dollars. "How about trying these in our mouths?" "They'll help," she replied, and she took one. "Be ready to tie your neckerchief over your nose, soon as we strike the alkali." The wisdom of this advice was evident when they started out across the snow-white flat. Every step stirred up clouds of alkali dust that hung about the fugitives like thick smoke. The impalpable powder penetrated their clothes, smarted in their eyes, and all but choked them, even behind the veiling neckerchiefs. Before they had half crossed the fearful dust flat Carmena was walking as slowly as the pony. At the far side she sank down beside a thick-stemmed cactus. Lennon, half delirious from fever, sought to spring off, with the vague idea of forcing her to ride. He succeeded only in tumbling upon the sand. The startled pony shied clear. With a smothered cry, Carmena leaped up to grasp his bridle. "Close call!" she gasped at Lennon. "If he'd made off--no show for us at all." Lennon was too far gone for speech. His canteen was already half empty. Carmena gave him a sip from her own and dragged him around until his head lay in the small blot of shade made by a cactus stem. Half an hour passed before he was able to get back into the saddle. But the rest appeared to have fully restored the girl's strength. She set off at a pace that again forced the pony into an occasional jog. After a time the sheltering ridge ran down into the sandy level of the desert. Yet Carmena continued to find a route protected by inequalities of the ground or by growths of cactus and thorn scrub from any eyes that might be peering across the Basin. As the sun sank nearer to the western rim of buttes and mesas she kept an ever closer watch to the rear. Her own and Lennon's canteens were again empty and her seemingly tireless stride was at last beginning to flag. By the time the lower edge of the sun touched the rim of the Basin the fugitives had come opposite a long range of broken hills. Carmena dragged herself wearily up over an out-thrust spur ridge. Lennon was swaying in the saddle, and his tongue, like hers, had begun to swell. But the girl did not offer to open the canteen on the saddlehorn.