The Indian led off into one of the gray notches between the tumbled streams of lava. These streams were about thirty feet high, a rotting mass of splintered lava, rougher than any other kind of roughness in the world. At the apex of the notch, where two streams met, a narrow gully wound and ascended. Gale caught sight of the dim, pale shadow of a one-time trail. Near at hand it was invisible; he had to look far ahead to catch the faint tracery. Yaqui led Diablo into it, and then began the most laborious and vexatious and painful of all slow travel. Once up on top of that lava bed, Gale saw stretching away, breaking into millions of crests and ruts, a vast, red-black field sweeping onward and upward, with ragged, low ridges and mounds and spurs leading higher and higher to a great, split escarpment wall, above which dim peaks shone hazily blue in the distance. He looked no more in that direction. To keep his foothold, to save his horse, cost him all energy and attention. The course was marked out for him in the tracks of the other horses. He had only to follow. But nothing could have been more difficult. The disintegrating surface of a lava bed was at once the roughest, the hardest, the meanest, the cruelest, the most deceitful kind of ground to travel. It was rotten, yet it had corners as hard and sharp as pikes. It was rough, yet as slippery as ice. If there was a foot of level surface, that space would be one to break through under a horse's hoofs. It was seamed, lined, cracked, ridged, knotted iron. This lava bed resembled a tremendously magnified clinker. It had been a running sea of molten flint, boiling, bubbling, spouting, and it had burst its surface into a million sharp facets as it hardened. The color was dull, dark, angry red, like no other red, inflaming to the eye. The millions of minute crevices were dominated by deep fissures and holes, ragged and rough beyond all comparison. The fugitives made slow progress. They picked a cautious, winding way to and fro in little steps here and there along the many twists of the trail, up and down the unavoidable depressions, round and round the holes. At noon, so winding back upon itself had been their course, they appeared to have come only a short distance up the lava slope. It was rough work for them; it was terrible work for the horses. Blanco Diablo refused to answer to the power of the Yaqui. He balked, he plunged, he bit and kicked. He had to be pulled and beaten over many places. Mercedes's horse almost threw her, and she was put upon Blanco Sol. The white charger snorted a protest, then, obedient to Gale's stern call, patiently lowered his noble head and pawed the lava for a footing that would hold.