314 COSMOS. 



How is tins mode of manifestation of volcanic activity, the 

 action of which I am describing, to be denominated ?* Have 

 we here to do with lava streams ? or only with semi-scorified 

 and ignited masses, which are thrown out unconnected, but 

 in chains pressed closely upon each other (as on Cotapaxi in 

 very recent times) ? Have the dikes of Yana Volcan and 

 Ansango been, perhaps, merely solid fragmentary masses, 

 which burst forth without any fresh elevation of temperature 

 from the interior of a volcanic conical mountain, in which 

 they lay loosely accumulated, and therefore badly supported, 

 their movement being caused by the concussion of an earth- 

 quake, impelled by shocks or falls, and giving rise to small 

 local earthquakes? Is no one of the three manifestations of 

 volcanic activity here indicated, different as they are, appli- 

 cable in this case? and have the linear accumulations of rock 

 detritus been upheaved upon fissures in the spots where they 

 now lie (at the foot and in the vicinity of a volcano) ? The 

 two dikes of fragments in this so slightly inclined plateau, 

 called Volcan de la Hacienda and Yana Volcan, which I 

 once considered, although only conjecturally, as cooled lava 

 streams, now appear to me, as far as I can remember, to 

 present but little in support of the latter opinion. In the 

 Volcan de Ansango, where the line of fragments may be 

 traced without interruption, like a river-bed, to the pumice 

 margins of two small lakes, the fall, or difference of level be- 

 tween Pinantura 1482 toises (9476 feet), andLecheyacu 1900 

 toises (12,150 feet), in a distance of about 7700 toises (49,239 

 feet), by no means contradicts what we now believe w r e know, 

 of the small average angles of inclination of lava streams. 

 From the difference of level of 418 toises (2674 feet), there 

 is an inclination of 3 6'. A partial elevation of the soil in 

 the middle of the floor of the valley would not appear to be 

 any hinderance, because the back swell of fluid masses im- 

 pelled up valleys has been observed elsewhere ; for example, 

 in the eruption of Scaptar Jokul in Iceland, in 1783 (Nau- 

 mann, Geognosie, bd. i., s. 160). 



The word lava indicates no peculiar mineral composition 

 of the rock ; and when Leopold von Buch says that every 



* " There are few volcanoes in the chain of the Andes," says Leo- 

 pold von Buch, "which have presented streams of lava, and none 

 have ever been seen around the volcanoes of Quito. Antisana, upon 

 the eastern chain of the Andes, is the only volcano of Quito upon 

 which M. de Humboldt saw, near the summit, something analogous to 

 a stream of lava ; this stream was exactly like obsidian" (Dcscr. des 

 lies Canaries, 1836, p. 468 and 488). 



