314 REACTION OP THE INTERIOR OF THE EARTH 



tivity, which have been alluded to, applicable in this 

 case? and have the linear collections of rocky frag- 

 ments been actually elevated over fissures at the places 

 where we now see them (at the foot or in the vicinity of 

 a volcano) ? The two walls of fragments (on the high 

 and little inclined plain) called Volcan de la Hacienda 

 and Yana Volcan, and which I formerly spoke of (con- 

 jecturally only) as cooled lava-streams, still appear to 

 me, speaking from recollection at so great a distance of 

 time, to lend but little support to the view referred to 

 in the last sentence. In the Volcan de Ansango, in 

 which the lines of fragments can be traced uninter- 

 ruptedly, like a river-bed, to the pumice-covered margins 

 of two small lakes, there is nothing in the angle of fall, 

 i.e. the difference of level between Pinantura (9477 

 feet) and Lecheyacu (12,150 feet), for a distance of 

 about 7700 toises (16,413 yards), inconsistent with the 

 present state of our knowledge as to the small average 

 angle of inclination in lava-currents. The difference of 

 level, 2673 feet, gives an inclination of 3 6'. A partial 

 rise of the ground in the middle of the lowest part need 

 not be regarded as an obstacle, as cases of fluid masses 

 overriding such rises have been observed ; for example 

 in the eruption of Skapta Jokul in Iceland, in 1783 

 (Naumann, Greognosie, Bd. i. s. 160). 



The word lava does not designate any particular 

 mineralogical composition of rock; and whereas Leopold 

 von Buch says that all is lava which flows in the inte- 

 rior of a volcano, and is capable by its fluidity of forming 

 fresh beds of deposit, I would add that fluidity is not 

 essential to such changes. Already, in the first de- 

 scription ( 449 ) of my attempt to reach the summit of 



