NO. 3 



SMITHSONIAN EXPLORATIONS, I915 



II 



Fig. 15. — Sidney and Stuart Walcott cutting out specimen near the Growler, 

 Norris Geyser Basin. They were driven back many times before the hot rock 

 was finally secured. Photograph by Walcott. 



Fig. 16. — Algal growth in cool pond where there was no mineral matter in 

 solution to be deposited. Photograph by Walcott. 



