274 PHYSICAL GEOGRAPHY. 



boiling water up the fissure or pipe E B, and a considerable quantity runs over the rim 

 of the basin. When the pressure on the steam in the upper part of the cavity is thus 

 diminished, it expands till all the water, D, is driven to E, the bottom of the pipe ; and 

 when this happens, the steam rushes up with great velocity, as on the opening of the 

 valve of a steam boiler. Mr. Lyell, upon the same principle, accounts for the eruption of 

 volcanoes, referring it to the agency of steam upon melted lava accumulated in cavi- 

 ties in the bowels of the earth a theory which, though not demonstrable, is invested 

 with a high degree of probability. Incidental notice may here be taken of some springs 

 which appear to boil, but are cold to the touch and to the thermometer. They are occa- 

 sioned by currents of pure air or gases being in connection with their waters. There is 

 one of this kind at Peroul, near Montpellier, which bubbles and heaves up furiously ; and 

 some parts of the river Etang, in the vicinity, exhibit the same appearance. Dr. Robin- 

 son found, in several dry places of the ground in that district, many small passages or 

 clefts, at the mouth of which he placed light bodies, such as feathers, straws, and leaves, 

 which were speedily blown aside. 



A remarkable spot was visited by Humboldt in South America, where phenomena of a 

 class similar to those of the ebullient springs appeared the eruption of water, mud, and 

 air from the surface. The scene of this exhibition was near the Indian village of Tur- 

 baco, in the neighbourhood of Carthagena a beautiful district adorned with luxuriant 

 vegetation. After pushing his way through thickets of palm-trees, he reached an open 

 space almost entirely devoid of verdure, called, by the natives, Los Volcanitos. They 

 affirmed that, according to a tradition preserved in the village, the ground had formerly 

 been ignited ; but that a monk had extinguished it by frequent applications of holy water, 

 and converted the fire volcano into a water volcano. The volcanitos consisted of several 

 small truncated cones, having a height of about twenty feet, and their circumference at 

 the base near eighty yards. At the top of each cone there was an aperture, about two 

 feet in diameter, filled with water, through which air-bubbles obtained a passage. Each 

 of the bubbles contained upwards of a cubic foot of elastic fluid; and their power of 

 expansion was often so great, that the water was projected over the brim of the cone. 

 Some openings by which air escaped were observed in the plain, without being sur- 

 rounded by any prominence of the ground. 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 the 

 water and mud was not higher than that of the atmosphere ; the latter having been 8 To , 

 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. Here, 

 botanising in the magnificent woods around, the traveller spent several happy days with 

 Bonpland the scientific companion of his journey, afterwards seized by the tyrant 

 Francia the subject of the following pleasing allusion, written in 1831 : "At Turbaco 

 we lived a simple and laborious life. We were young ; possessed a similarity of taste and 

 disposition ; looked forward to the future with hope; were on the eve of a journey which 

 was to lead us to the highest summits of the Andes, and bring us to volcanoes in action 

 in a country continually agitated by earthquakes ; and we felt ourselves more happy than 

 at any other period of our distant expedition. The years which have since passed, not 

 all exempt from griefs and pains, have added to the charms of these impressions ; and I 

 love to think that, in the midst of his exile in the southern hemisphere, in the solitudes 

 of Paraguay, my unfortunate friend, M. Bonpland, sometimes remembers with delight 

 our botanical excursions at Turbaco the little spring of Torecillo the first sight of 



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