Air bubbles. 



VOLCANCITOS OF TURBACO. 273 



into pentagonal and lieptagonal prfsms. Tlie volcancitos CHAP.xxil 

 consist of fifteen or t^venty small truncated cones rising j^y^"^ 

 in the middle of this area, and having a height of from canoes. 

 19 to 25 feet. The most elevated were on the southern 

 side, and their circumference at the base was from 78 to 

 85 yards. On climbing to the top of these mud- 

 volcanoes, they found them to be terminated by an 

 aperture from IG to 30 inches in diameter, filled with 

 water, through which air-bubbles obtained a passage ; 

 about five explosions usually taking place in two mi- 

 nutes. The force with which the air rises would lead 

 to the supposition of its being subjected to considerable 

 pressure, and a rather loud noise was heard at intervals, 

 preceding the disengagement of it fifteen or eighteen 

 seconds. Each of the bubbles contained from 12 to 14^ 

 cubic inches of elastic fluid, and their power of expan- 

 sion was often so great that the water was projected 

 beyond the crater, or flowed over its brim. Some of 

 the openings by which air escaped were situated in the 

 plain without being surrounded by any prominence of 

 the ground. It was observed that when the apertures, 

 which are not placed at the summit of the cones, and 

 are enclosed by a little mud- wall from 10 to 15 inches 

 high, are nearly contiguous, the explosions did not take 

 place at the same time. It would appear that each neception 

 crater receives the gas by distinct canals, or that these, °^s^^ 

 terminating in the same reservoir of compressed air, 

 oppose greater or less impediments to the passage of the 

 aeriform fluids. The cones have no doubt been raised 

 by these fluids, and the dull sound that precedes the 

 disengagement of them indicates that the ground is 

 hollow. The natives asserted that there had been no 

 observable change in the form and number of the cones 

 for twenty years, and that the little cavities are filled with 

 water even in the driest seasons. The temperature of 

 this liquid was not higher than that of the atmosphere ; 

 the latter having been 81*5°, and the former 80"6'^ or 

 81°, at the time of Humboldt's visit. A stick could 

 easily be pushed into the apertures to the depth of six 



