Saying which, he took up the bridles, and tossed them over the crest of the cliff; then ascended himself, helping Kearney. There was no path; but some projections of the rock--ledges, with the stems of cactus plants growing upon their--made the ascent possible. The Texan swarmed up after, with hunchback at his heels; as he got upon the top, turning suddenly round, laying hold of the chain, and with a "Jee up," hoisting the creature feet foremost! Another second and they were all out of sight; though not a second too soon. For as they turned their backs upon the cliff, they could hear behind, on the farther edge of the thicket through which they had passed, the signal calls of a cavalry bugle. CHAPTER THIRTY SIX. THE PEDREGAL. Interesting as is the Mexican Valley in a scenic sense, it is equally so in the geological one; perhaps no part of the earth's crust of like limited area offering greater attractions to him who would study the lore of the rocks. There he may witness the action of both Plutonic and Volcanic forces, not alone in records of the buried past, but still existing, and too oft making display of their mighty power in the earthquake and the burning mountain. There also may be observed the opposed processes of deposition and denudation in the slitting up of great lakes, and the down wearing of hills by tropical rain storms, with the river torrents resulting from them. Nor is any portion of this elevated plateau more attractive to the geologist than that known as "El Pedregal"; a tract lying in its south-western corner, contiguous to the Cerro de Ajusco, whose summit rises over it to a height of 6,000 feet and 13,000 above the level of the sea. It is a field of lava vomited forth from Ajusco itself in ages long past, which, as it cooled, became rent into fissures and honey-combed with cavities of every conceivable shape. Spread over many square miles of surface, it tenders this part of the valley almost impassable. No wheeled vehicle can be taken across it; and even the Mexican horse and mule--both sure-footed as goats--get through it with difficulty, and only by one or two known paths. To the pedestrian it is a task; and there are places into which he even cannot penetrate without scaling cliffs and traversing chasms deep and dangerous. It bristles with cactus, zuccas, and other forms of crystalline vegetation, characteristic of a barren soil. But there are spots of great fertility--hollows where the volcanic ashes were deposited--forming little _oases_, into which the honest Indian finds his way for purposes of cultivation. Others less honest seek refuge in its caves and coverts, fugitives from justice and the gaols--not always criminals, however, for within it the proscribed patriot and defeated soldier oft find an asylum.