14 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL, 66 
Fic. 20.—Illustration of algal growth in rapidly moving hot water in run-off 
from hot spring shown by Fig. 19. White siliceous deposit is made over and 
through algal growth, latter being gradually replaced and changed from soft 
gelatinous, spongy mass to hard siliceous permanent deposit. Photograph by 
Walcott. 
1 
Fic. 21.—Cream-colored siliceous deposit in run-off from Artemisia Geyser, 
Upper Geyser Basin. Photograph taken looking down through the water. 
Photograph by Walcott. 
