334 ELEMENTARY GEOLOGY 
blocks, that travel upon it is impossible. Among the 
Hawaiian Islands this rough surfaced lava flow is 
Fic. 200. 
A lava flow in Hawaii. 
called aa (Fig. 201), while the smooth surfaced lava, 
which has cooled with- 
out breaking, is called 
pahoehoe (Fig. 202). 
Both kinds may come 
from the same flow. 
Toward the last of 
the lava flow, move- 
ment is scarcely per- 
ceptible, and for weeks 
“3 
it proceeds forward 
Fig. 201, very slowly. During 
Rough aa surface at the end of a lava flow ° : 
near Mt. Shasta. this time one may 
