1832-3.) TUBES FORMED BY LIGHTNING. 59 
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 eonquest, 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 
de] 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. 
