1832-3.] TUBES FORMED BY LIGHTNING. 69 



the last species, as it never occurs southward of lat. 41°. Azara 

 states that there exists a tradition that these birds, at the time of 

 the conquest, were not found near Monte Video, but that they 

 subsequently followed the inhabitants from more northern dis- 

 tricts. At the present day they are numerous in the valley of 

 the Colorado, which is three hundred miles due south of Monte 

 Video. It seems probable that this additional migration has 

 happened since the time of Azara. The Gallinazo generally 

 prefers a humid climate, or rather the neighbourhood of fresh 

 water ; hence it is extremely abundant in Brazil and La Plata, 

 while it is never found on the desert and arid plains of Northern 

 Patagonia, excepting near some stream. These birds frequent 

 the whole Pampas to the foot of the Cordillera, but I never saw 

 or heard of one in Chile : in Peru they are preserved as scaven- 

 gers. These vultures certainly may be called gregarious, for 

 they seem to have pleasure in society, and are not solely brought 

 together by the attraction of a common prey. On a fine day a 

 flock may often be observed at a great height, each bird wheel- 

 ing round and round without closing its wings, in the most 

 graceful evolutions. This is clearly performed for the mere 

 pleasure of the exercise, or perhaps is connected with their matri- 

 monial alliances. 



I have now mentioned all the carrion-feeders, excepting the 

 condor, an account of which will be more appropriately intro- 

 duced when we visit a country more congenial to its habits than 

 the plains of La Plata. 



In a broad band of sand-hillocks which separate the Laguna 

 del Potrero from the shores of the Plata, at the distance of a few 

 miles from Maldonado, I found a group of those vitrified, silice- 

 ous tubes, which are formed by lightning entering loose sand. 

 These tubes resemble in every particular those from Drigg in 

 Cumberland, described in the Geological Transactions.* The 

 sand-hillocks of Maldonado, not being protected by vegetation, 

 are constantly changing their position. From this cause the 



* Geolog. Transact., vol. ii. p. 528. In the Philosoph. Transact. (1790, 

 p. 294) Dr. Priestley has described some imperfect siliceous tubes and a melted 

 pebble of quartz, found in digging into the ground, under a tree, where a 

 man had been killed by lightning. 



