186 8. CRUZ, PATAGONIA, [cHap. Ix, 
proclaim throughout the district to the whole family of carrion- 
feeders, that their prey is at hand ? 
When the condors are wheeling in a flock round and round 
any spot, their flight is beautiful. Except when rising from the 
ground, I do not recollect ever having seen one of these birds 
flap its wings. Near Lima, I watched several for nearly half an 
hour, without once taking off my eyes: they moved in large 
curves, sweeping in circles, descending and ascending without 
giving a single flap. As they glided close over my head, I in- 
tently watched from an oblique position, the outlines of the sepa- 
rate and great terminal feathers of each wing ; and these separate 
feathers, if there had been the least vibratory movement, would 
have appeared as if blended together; but they were seen dis- 
tinct against the blue sky. The head and neck were moved fre- 
quently, and apparently with force; and the extended wings 
seemed to form the fulcrum on which the movements of the 
neck, body, and tail acted. If the bird wished to descend, the 
wings were for a moment collapsed ; and when again expanded 
with an altered inclination, the momentum gained by the rapid 
descent seemed to urge the bird upwards with the even and 
steady movement of a paper kite. In the case of any bird soar- 
ing, its motion must be sufficiently rapid, so ‘that the action of 
the inclined surface of its body on the atmosphere may counter- 
balance its gravity. The furce to keep up the momentum of a 
body moving in a horizontal plane in the air (in which there is 
so little friction) cannot 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 over 
inountain and river. 
April 29th From some, high Jand we hailed with joy 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 on slowly, for we found 
the river-course very tortuous, and strewed with immense frag- 
ments of various ancient slaty rocks, and of granite. The plain 
bordering the valley had here attained an elevation of about 
