12 
MUSEUM BULLETIN NO. 4. 
be noted that Martin (p. 174) speaks of a fragment the size of 
a brick having travelled through the air to a distance of fifteen 
miles from the volcano. Doubtless much of the finer ash and 
dust from the Crowsnest eruptions were carried out of the zone 
of deposition of larger fragments by air and water currents. 
The volume of material ejected from Katmai is given 
(p. 167) as 4*9 cubic miles, extending over an area of many 
thousand square miles, as against the fifty cubic miles of the 
Crowsnest tuffs and breccias spread over 700 square miles. 
Tomboro is supposed by some (p. 165) to have ejected fifty 
cubic miles of material in a single eruption, again spread over 
thousands of square miles. A more conservative estimate 
gives twenty-eight cubic miles. 
Even allowing for ash carried away by currents, it is not 
probable that a much greater area than is now represented by 
volcanic sediment was originally effected by the out-burst, but 
instead, it would appear that a large volume of material in 
comparison to the area involved, was deposited. The thinness 
of individual beds, and their alternation in character indicates 
that the formation was built up by successive eruptions none 
of which were of very great magnitude. The absence of flows 
or sills shows that the eruptions were dominantly of the explosive 
type. 
It thus seems apparent that the individual eruptions were 
not of great violence, and that a preliminary explosion during 
Dakota time fore-shadowed the approach of the Crowsnest 
epoch, during which continual explosions on a moderate scale 
took place. The time of eruption was probably short, reasoning 
from the amount of material sent out during a single out-burst 
of modern volcanoes. The explosive period ceased abruptly, 
and was followed by a rather rapid subsidence, as has already 
been pointed out. 
Location of Vents. 
No recognizable volcanic vents have been observed in any 
of the outcrops studied. This is not altogether surprising when 
it is remembered that only a small portion of the formation is 
