J 832-3. 



CARRION HAWKS. 



69 



scavengers. 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 wheeling round and round without closing its 

 wings, in the most graceful evolutions. This is clearly done 

 for sport-sake, 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 

 introduced 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 La- 

 guna del Potrero from the shores of the Plata, at the distance 

 of a few miles from Maldonado, I found a group of those 

 vitrified, siliceous tubes, which are generally supposed to 

 have been formed by lightning entering the 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 tubes projected above the surface ; and nume- 

 rous fragments lying near, showed that they had formerly 

 been buried to a greater depth. Four, sets entered the sand 

 perpendicularly : by working with my hands I traced one of 

 them two feet deep ; and some fragments which evidently 

 had belonged to the same tube, when added to the other 

 part, measured five feet three inches. The diameter of the 

 whole was nearly equal, and therefore we must suppose that 

 originally it extended to a much greater depth. These dimen- 

 sions are however small, compared to those of the tubes 

 from Drigg, one of which was traced to a depth of not less 

 than thirty feet. 



The internal surface is completely vitrified, glossy, and 

 smooth. A small fragment examined under the micro- 



* Geolog. Transact,, vol. ii.. p, 528. 



