When the condors are wheeling in a flock round an round any spot, their flight is beautiful. Except when risin from the ground, I do not recollect ever having seen on of these birds flap its wings. Near Lima, I watched severa for nearly half an hour, without once taking off my eyes they moved in large curves, sweeping in circles, descendin and ascending without giving a single flap. As they glide close over my head, I intently watched from an oblique position, the outlines of the separate and great terminal feather of each wing; and these separate feathers, if there had bee the least vibratory movement, would have appeared as i blended together; but they were seen distinct against th blue sky. The head and neck were moved frequently, an apparently with force; and the extended wings seemed t form the fulcrum on which the movements of the neck, body and tail acted. If the bird wished to descend, the wing were for a moment collapsed; and when again expande with an altered inclination, the momentum gained by th rapid descent seemed to urge the bird upwards with th even and steady movement of a paper kite. In the case o any bird soaring, its motion must be sufficiently rapid s that the action of the inclined surface of its body on th atmosphere may counterbalance its gravity. The force t keep up the momentum of a body moving in a horizonta plane in the air (in which there is so little friction) canno be great, and this force is all that is wanted. The movement of the neck and body of the condor, we must suppose is sufficient for this. However this may be, it is truly wonderful and beautiful to see so great a bird, hour after hour without any apparent exertion, wheeling and gliding ove mountain and river
April 29th. -- From some high land we hailed with jo the white summits of the Cordillera, as they were seen occasionally peeping through their dusky envelope of clouds During the few succeeding days we continued to get o slowly, for we found the river-course very tortuous, an strewed with immense fragments of various ancient slat rocks, and of granite. The plain bordering the valley ha here attained an elevation of about 1100 feet above the river and its character was much altered. The well-rounded pebbles of porphyry were mingled with many immense angula fragments of basalt and of primary rocks. The first of thes erratic boulders which I noticed, was sixty-seven miles distant from the nearest mountain; another which I measure was five yards square, and projected five feet above th gravel. Its edges were so angular, and its size so great, tha I at first mistook it for a rock _in situ_, and took out my compass to observe the direction of its cleavage. The plain her was not quite so level as that nearer the coast, but yet i betrayed no signs of any great violence. Under these circumstances it is, I believe, quite impossible to explain th transportal of these gigantic masses of rock so many mile from their parent-source, on any theory except by that o floating icebergs.
During the two last days we met with signs of horses, an with several small articles which had belonged to the Indian -- such as parts of a mantle and a bunch of ostrich feathers -- but they appeared to have been lying long on the ground Between the place where the Indians had so lately crosse the river and this neighbourhood, though so many mile apart, the country appears to be quite unfrequented. At first considering the abundance of the guanacos, I was surprise at this; but it is explained by the stony nature of the plains which would soon disable an unshod horse from taking par in the chase. Nevertheless, in two places in this very centra region, I found small heaps of stones, which I do not thin could have been accidentally thrown together. They wer placed on points, projecting over the edge of the highest lav cliff, and they resembled, but on a small scale, those nea Port Desire.
May 4th. -- Captain Fitz Roy determined to take the boat no higher. The river had a winding course, and was ver rapid; and the appearance of the country offered no temptation to proceed any further. Everywhere we met with th same productions, and the same dreary landscape. We wer now one hundred and forty miles distant from the Atlantic and about sixty from the nearest arm of the Pacific. Th valley in this upper part expanded into a wide basin, bounde on the north and south by the basaltic platforms, and fronte by the long range of the snow-clad Cordillera. But w viewed these grand mountains with regret, for we wer obliged to imagine their nature and productions, instead o standing, as we had hoped, on their summits. Besides th useless loss of time which an attempt to ascend the river an higher would have cost us, we had already been for som days on half allowance of bread. This, although reall enough for reasonable men, was, after a hard day's march rather scanty food: a light stomach and an easy digestio are good things to talk about, but very unpleasant in practice