TRUE VOLCANOES. 335 



have not, however, flowed out in streams like lava, but have 

 probably been expelled at fissures on the declivity of the 

 previously upheaved, bell-shaped mountain." This genetic 

 explanation might find abundant support in the assumptions 

 of Boussingault, who regards the volcanic cones themselves 

 " as an accumulation of angular trachytic fragments, upheaved 

 in a solid condition, and heaped up without any order. As 

 after the upheaval the broken rocky masses occupy a greater 

 space than before they were shattered, great cavities remain 

 amongst them, movement being produced by pressure and 

 shock (the action of the volcanic vapour-force being ab- 

 stracted)." I am far from doubting the partial occurrence of 

 such fragments and cavities, which become filled with water 

 in the Nevados, although the beautiful, regular, and, for the 

 most part, perfectly perpendicular trachytic columns of the 

 Pico de los Ladrillos, and Tablahuma on Pichincha, and, 

 above all, over the small basin. Yana-Cocha on Chimborazo, 

 appear to me to have been formed on the spot. My old 

 and valued friend, Boussingault, whose chemico-geognostic 

 and meteorological opinions I am always ready to adopt, 

 regards what is called the Yolcan de Ansango, and what 

 now appears to me as an eruption of fragments from two 

 small lateral craters (on the western Antisana. below Chus- 

 sulongo) as upheavals of blocks 20 upon long fissures. As 

 26 \y e differ entirely with regard to the pretended stream of 

 Antisana towards Pinantura. I regard this stream (coulee] as a recent 

 upheaval analogous to those of Calpi (Yana Urcu). Pisque, and Jorullo. 

 The trachytic fragments have acquired a greater thickness towards the 

 middle of the stream. Their stratum is thicker towards Pinantura 

 than at points nearer Antisana. The fragmentary condition is an 

 effect of local upheaval, and in the Cordillera of the Andes earth- 

 quakes may often be produced by heaping up " (letter from M. Bous- 

 eingault, dated August, 1834). See page 270. In the description 

 of his ascent of Chimborazo (December, 1831), Boussingault says : 

 " The mass of the mountain consists, in my opinion, of a 

 heap of trachytic ruins piled up on each other without any order. 

 These trachytic fragments of a volcano, which are often of enormous 

 size, are upheaved in the solid state ; their edges are sharp, and nothing 

 indicates that they had been in a fused or even a softened condition. 

 Nowhere, on any of the equatorial volcanoes, do we observe anything 

 that would allow us to infer a lava-stream. Nothing has ever been 

 thrown out from these craters except masses of mud, elastic fluids and 

 ignited, more or less scorified trachytic blocks, which have frequently 

 been scattered to considerable distances" (Hurnboldt, Kleinere Schriften t 



