September 5th, at an early hour, we were awoke by Orkeke's marching harangue; and after coasting the hills bordering the valley for a few miles, bade adieu to the valley of the Rio Chico, and struck into a gorge of the northern hills, leading into an uneven valley lying between low irregular hills of decomposed lava, which we followed, passing several small lagoons in the lower hollows, around which there was invariably a yellow description of clay. The hills were everywhere covered with scrub, and presented a wild, bleak appearance, the grey rocks only appearing now and then. After some hours' travelling through this dismal district in a north-west course, we emerged on a large plain at the western side, bounded by a range of hills 1,000 feet high, forming a spur of the Cordillera. The weather was stormy, and we could only catch occasional glimpses, through the driving clouds and snow-storms, of the loftier peaks of the more distant mountains. Our expedition in search of wild horses was, of course, after the recent troubles, abandoned; and forced marches, to escape the Southern Indians, in the event of their following from Santa Cruz, were the order of the day. Hunting, however, was resumed by the unwounded, and several ostriches were caught during the day. Towards evening the encampment was fixed near a lagoon, the environs of which were barren, and destitute of anything except a small low shrub which served for firewood. Although the wind was northerly, it was bitterly cold; and as I had for some days past adopted the native costume--keeping my 'store clothes' stowed away under charge of Mrs. Orkeke--I felt it exceedingly. The 6th, 7th, and 8th of September were occupied in making forced marches northward, accompanied by the usual hunting; and although both parties continued armed, and appeared to be rather suspicious of each other, things went on pretty smoothly. The country traversed on the 6th and 7th was a large arid plain, dotted with a few stunted shrubs, enclosed by the before-mentioned spur of the Cordillera on the western side, and on the east by a low range of sandy-looking hills. The whole of this plain was strewn with small pebbles of porphyry, quartz, silica, and obsidian; also with small pieces of silicified wood. On the 8th we crossed the spur by a pass walled on either hand with rocks of vesicular lava. Here we halted for a quarter of an hour, and everyone broke off pieces of stone suitable for making hand-balls for bolas. The descent on the western side was no easy matter, the declivity being strewn with large masses of rock and loose boulders, and the wind blowing bitterly cold, and with such force that some of the women's horses could hardly face it. Ultimately all managed to reach a spacious elevated pampa, on the western side of which, some fifteen leagues off, rose the Cordillera of the Andes. In the pass I observed several large pieces of obsidian, so clear and peculiarly round-shaped that I at first imagined that a demijohn had been carried thither by some previous party and broken. Of this the women gathered some pieces, to serve as scrapers for cleaning guanaco skins. We traversed the usual barren high pampa--interspersed with low shrubs, coarse grass, and here and there an incense bush of considerable size, which afforded a moment's shelter from the cutting wind--for some distance, till we at length reached a cliff, below which lay a grassy plain, watered by a small, rapid stream. About thirty miles in the background were visible the lofty mountains of the Cordillera. The inviting appearance of the pasture determined us to remain for a couple of days to rest the horses, after the unusually long marches of the preceding days. The following day was occupied chiefly in making hand-balls for bolas from the soft porous stone obtained in the rocky pass. Towards noon a frightful gale of wind sprang up, which blew down most of the toldos; but ours, thanks to the strength of arm of Mrs. Orkeke, who had securely fixed the poles, remained firm, only one or two of the poles being broken. The river, here flowing in an eastward direction, was the first stream met with since leaving the valley of the Rio Chico. In the descent to it, the bench formation, although recognisable, was not so much marked as in many of the other rivers. After two days' rest, we resumed our journey; and having traversed the grassy valley for, perhaps, a mile, ascended a slight ridge to a higher plain of the usual sterile nature, in which the first ostrich eggs met with were found. Our course was directed nearly north-west, to a range of hills 800 feet in height; on their summit was a plateau strewn with large stones and rocks.