4 The American Geologist. January, looi. 
With due allowance for the single disturbing influence of 
the wind upon the summit of the mighty fountain, it is evident 
that the very perfect symmetry of the main portion of the 
rim could have been produced only by an extremely regular 
fall of the spreading fountain of ejecta at a uniform and un- 
varying distance from the vent. Any interruption or inter- 
mission would have so disturbed that precise uniformity of 
projection as to have piled the falling tufif in irregular posi- 
tions. The beautiful symmetry of the crater is a powerful 
witness of its sudden and rapid formation. It forbids any 
other conception. 
"Sly second evidence of the brevity of the eruption which 
created the crater-cone is derived from an arithmetical compu- 
tation of the time required to deposit the actual mass of the 
cone by a fountain of adequate hight to deliver its ejecta upon 
the existing rim of the bowl. Data are easily secured for a 
sufficiently approximate estimate of the time to show that it 
could have occupied a very few hours at most. Let us first 
compute the solid contents of the tufif deposited. The average 
diameter of the bowl is about 5,000 feet. Two-thirds of the 
perimeter is 450 feet high, to which 50 feet may be added on 
account of the average depth of sea at the distance from the 
shore, where the eruption occurred. The other third of the 
perimeter was occupied by a conical mass probably 1,000 feet 
high, but standing in perhaps 250 feet depth of sea. Estimat- 
ing this cone as 1,250 feet high, with 5,000 feet diameter of 
base, its solid content would be about 8,000,000,000 cubic feet. 
The contents of the other two-thirds of the perimeter would 
be about 5,000,000,000 feet, making with the cone a mass of 
13,000,000,000 cubic feet of tuff in the entire crater. 
A similar result is obtained by assuming a base equivalent 
to 5,000 feet square, and an average hight of 500 feet, which 
gives a solid content of twelve and a half billions of cubic feet. 
It is evident that such an estimate is sufficiently large. 
Now, to have ejected the whole mass in five hours would 
have required an emission from the vent of two and a half bil- 
lions of cubic feet of tuff in an hour, or of 694,444, feet in 
one second. Supposing the vent to have a sectional area of 
2,000 feet, which I believe to be much too small, the velocity of 
emission would be only 347 feet in a second, which is equiva- 
