Russell — Massive-Solid Volcanic Eruptions. 259 



or more feet high, as well as massive escarpments and smootli 

 fissure-walls of the same material. In many places the glass 

 passes into a highly scoriaceous rock, resembling a coarse black 

 pumice. Along the sides and at the distal end of the lava 

 stream it terminates in precipitous escarpments, exceedingly 

 difficult to climb, from 50 to 80 feet high. The slope down 

 which the lava flowed has a descent by estimate of at least 500 

 feet to a mile, and the fact that the stream halted on such an 

 incline and cooled with essentially vertical borders, shows that 

 it was excessively viscous at the time it was spread out. 



The feature of chief interest in connection with the volcano 

 in question is a tower- like mass of crags of gray stony or gran- 

 ular homogeneous augite-andesite (as determined by F. C. 

 Calkins, of the U. S. Geological Survey), without either obsi- 

 dian or scoria and in which there is a notable absence of a 

 "flow-structure," which rises to a height of about 250 feet 

 above the crater's floor. The sides of the central mass of 

 crags, as may be judged from the accompanying photograph, 

 are precipitous, and allowing for the blocks that have 

 fallen, must at one time have been nearly vertical. The 

 lava of which the crags are composed is fresh in appearance, 

 there being no discoloration of the surface, and scarcely a 

 lichen has taken root upon it. It exhibits no evidence of there 

 having been a tendency to flow laterally at the time it was 

 upraised, and although irregularly jointed is not columnar. 



A peculiar feature of the floor of the crater at the base of 

 the crags described above is that the lapilli, of which it is com- 

 posed, are in irregular heaps and piles with steep-sided depres- 

 sions between, the variations in height between the hills and 

 hollows being from 10 to fully 30 feet. The topography of 

 this surface is surprisingly like that of certain glacial moraines, 

 but its roughness is due in part to the occurrence, at a late stage 

 in the activity of the volcano, of many mild steam explosions 

 in the fragmental material of which it is superficially composed, 

 and in part to the formation of fissures in the rocks beneath, 

 which permitted the loose material resting on them to subside 

 irregularly. About the outer margin of the floor of the crater 

 from its eastern around its southern to its northwest portion, 

 there is a belt about 150 feet wide composed of obsidian and 

 black scoria, which resembles the surface of the associated lava 

 flow. This partially encircling belt of large fragments margin- 

 ing the crater's bottom is due to motion which took place after 

 the lava of which it is composed became solid, but whether the 

 motion was of the nature of an underflow in still viscous mate- 

 rial beneath a rigid crust, or was an upward movement of the 

 entire lava column within the crater, is uncertain. I am 

 inclined, however, to the latter opinion. 



