97 



This engraving was executed from a sketch made 

 by one of our friends, Mr. Lewis de Rieux. 

 This young artist, with whom we ascended the 

 river Magdalena, was then attending his father, 

 who, under the administration of Mr. d'Urquijo, 

 was charged with the inspection of the bark trees 

 of Santa-Fe\ 



In the centre of a vast plain, bordered by 

 bromelia karatas, are eighteen or twenty small 

 cones, in height not above seven or eight me- 

 tres. These cones are formed of a blackish gray 

 clay, and have an opening at their summits 

 filled with water. On approaching these small 

 craters, a hollow but very distinct sound is heard 

 at intervals, fifteen or eighteen seconds previous 

 to the disengagement of a great quantity of air. 

 The force with which this air rises above the 

 surface of the water may lead us to suppose, that 

 it undergoes a great pressure in the bowels of 

 the Earth. I generally reckoned five explosions 

 in two minutes : and this phenomenon is 

 often attended with a muddy ejection. The 

 Indians assured us, that the forms of the cones 

 undergo no visible change in a great number of 

 years ; but the ascending force of the gas, and 

 the frequency of the explosions, appear to vary 

 according to the seasons. I found by analyses 

 made by means both of nitrous gas and of 

 phosphorus, that the disengaged air scarcely 



VOL. xiv. h 



