CARRION-VULTURES. 239 



from an oblique position the outlines of the separate 

 and great terminal feathers of each wing ; and these 

 separate feathers, if there had been the least vibra- 

 tory movement, would have appeared as if blended 

 together; but they were seen distinct against the 

 blue sky. The head and neck were moved fre- 

 quently, and apparently with force ; and the extend- 

 ed 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 exjaanded with 

 an altered inclination, the momentum gained by 

 the rapid descent seemed to urge the bird upwards 

 wdth the even and steady movement of a paper kite. 

 In the case of any bird soaring, 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 force to keep up the mo- 

 mentum 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 ti-uly wonderful and beautiful to see 

 so great a bird, hour after hour, without any ap- 

 parent exertion, wheeling and gliding over mount- 

 ain and river. 



Ajnil 29th. — From some high land 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 fragments of various ancient slaty rocks, 

 and of granite. The plain bordering the valley 

 had here attained an elevation of about 1100 feet 



