52Q 



PKOCEEDINGS OF THE GEOLOGICAL SOCIETY. 



[Feb. 2, 



confidence. M. de Buch himself describes the steep slopes of the Peak 

 of Teneriife as encrusted with numerous currents of glassy lava 

 (obsidian)*, which he admits to have been erupted near the summit 

 and to have flowed down the sides of the cone, an observation which 

 alone should have led him to discredit De Beaumont's theory of 

 consolidation. 



Again, he speaks of some of the cones of Lanzarote, which he admits 

 to have been formed by eruption, as having vast massive basaltic 

 currents of lava ^' like black glaciers precipitating themselves from 

 the summit to the base of each cone." He represents himself as 

 painfully climbing for an hour and a half up the steep and rugged sur- 

 face of one of these " cheires," to reach the high margin of the crater. 

 Humboldt describes himself as doing the same thing in his attempt 

 to reach the source of the great lava-stream of Jorullo on the sum- 

 mit of the cone from whose crater it issued ; and in the drawing 

 he gives of it, the bulky promontory of basaltic lava-rock is repre- 

 sented as leaning against the cone at an angle of more than 35°. 

 (See fig. 1, p. 510.) Even M. de Beaumont is forced to recognize 

 the lava-streams that have hardened on the steep slope of the cone 

 of Etna as eruptive. He says, " La croute de I'Etna est evidemment 

 une croute d'eruptionf " — which indeed it is, as may be seen in 

 fig. 10. 



Fig. 10. — View of the Summit of Etna, and the Lavas that encrust 

 its slojpes towards the Val del Bove. (After W. Sartorius de Wal- 

 tershausen.) 



M. de Beaumont admits the same of Teneriffe (the Peak), which 

 he actually classes as a cone of eruption, thereby differing from de 

 Buch, and, in my view, giving up his whole theory, since the slopes of 

 the Peak have a higher angle of elevation than those of the outer 

 " cirque," or of the mass of Etna. (See fig. 4, p. 512.) 



Mr. Darwin gives a description, among the numerous unquestionable 

 craters of eruption iu the Galapagos Islands, of five in Albemarle 

 Isle, from 4700 to 3720 feet in height, with craters three miles and 

 upwards in diameter, ^'over the lips of which great caldrons, or from 

 orifices on their summits, deluges of black lava have flowed down their 

 steep and naked sides." In all these cases the lavas clearly conso- 

 Hdated in sheets, beds, or bulky masses, at very high angles of incU- 

 * Canaries, p. 186. t Memoires, vol. iii. p. 207. 



