470 J. LeConte—Formation of the 
can fora moment imagine that these immense floods of lava 
have issued from craters. The lava floods of the Sierra and 
Cascade ranges are, it seems to me, among the most extra- 
ordinary in the world. Commencing in middle California as 
immense but separate lava streams, in northern California it 
becomes an almost universal flood several hundred feet thick ; 
in Oregon the flood becomes universal, and at least 2,000 feet 
thick, and this continues through Washington Territory and 
into British Columbia, how far I know not. An area 700 to 
By this theory, as by every other theory of mountain for- 
mation, it is necessary to suppose that there have been in the 
history of the earth periods of comparative quiet, during which 
of revolution- 
range, where it is cut through by the Columbia river and its 
. Jerlaid ern boulder drift 
Since that time we have been in what might be called a crater- 
ly d 
* Richthofen, th en, Natural ‘System of Volcanic Rocks : Memoirs of Cal. Acad. 
vol. i, part 2d. 
soon to give th der si i 
+ I hope give the evidence of this in a separate co tion 
