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SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 66 



Fig. 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. 



Fig. 21. — Cream-colored siliceous deposit in run-off from Artemisia Geyser, 

 Upper Geyser Basin. Photograph taken looking down through the water. 

 Photograph by Walcott. 



