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320 VOLCANCITOS AND VEGETATION. 
mud wall from 10 to 15 inches high, are nearly conti- 
guous, the explosions did not take place at the same 
time. It would appear that each crater receives 
the gas by distinct canals, or that these, terminat- 
ing in the same reservoir of compressed air, op- 
pose 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 lat-_ 
ter having been 8]-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 or 
seven feet, and the dark-coloured clay or mud was 
exceedingly soft. An ignited body was immediately 
extinguished on being immersed in the gas collected — 
from the bubbles, which was found to be pure azote. 
The stay which our travellers made at Turbaco 
was uncommonly agreeable, and added greatly to 
their collection of plants. “Even now,” says Hum- 
boldt, writing in 1831, “after so long a lapse of 
time, and after returning from the banks of the Obi — 
and the confines of Chinese Zungaria, these bam- 
boo thickets, that wild luxuriance of vegetation, 
those orchidee covering the old trunks of the ocotea 
and Indian fig, that majestie view of the snowy 
mountains, that light mist filling the bottom of the 
valleys at sunrise, those tufts of gigantic trees rising 
like verdant islets from a sea of vapours, incessantly 
present themselves to my imagination. At Turbaco 
uj, 
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