194 REACTION OF THE INTERIOR OF THE EARTH 



mass, but to that of currents of air rising from lower 

 depths. There is, moreover, at the foot of the Chimbo- 

 razo, at an elevation of 9500 feet, not far from the 

 village of Calpi, a small crater of eruption called 

 Yana-Urcu, which, in the middle of the 15th century, 

 appears to have been in a state of activity, as is also 

 indicated by its black scoriaceous rock (augitic por- 

 phyry.) () 



The aridity of the plain out of which the Chimborazo 

 rises, and the existence of the subterranean brook 

 of which the rushing sound is heard under the above- 

 named volcanic hill Yana-Urcu, led both Boussingault 

 and myself, ( 267 ) at very different times, to consider that 

 the waters proceeding from the daily melting of the 

 enormous masses of snow at their lower limit, sink down 

 into deep clefts and hollows below the upheaved volca- 

 noes. These waters produce continual refrigeration 

 in the strata through which they sink. But for this 

 agency the entire -dolerite and trachyte mountains, even 

 at times when there is no indication of any proximate 

 eruption, woidd have a still higher internal temperature 

 imparted to them by the ever-acting primeval volcanic 

 source of heat, which, perhaps, is not at an equal depth 

 in all zones of the earth. Thus, in the conflict between 

 heating and cooling causes, the existence of a perpetual 

 flow of heat both upwards and downwards may be most 

 particularly assumed where the solid parts of the earth's 

 surface rise high into the atmosphere. 



Mountains and high summits, however, regarded 

 relatively to the area which they occupy, are but a very 

 small phenomenon in the relief-form (or vertical confi- 

 guration of the dry land) ; and, moreover, almost two 



