THE GROWTH OF STALAGMITES AND STALACTITES 125 



in evaporation, accompanied by a slight movement of the drip/ 

 This caused a more rapidly growing stalagmite of a little greater 

 diameter. 



Several stalactites and stalagmites are now under observation 

 in Marengo Cave, Indiana,^ but their growth is probably slow. 



CONCLUSIONS 



An approximation method for determining the age of stalag- 

 mites has been developed. 



Symmetry in a stalagmite indicates constant growth conditions. 



Stalagmites with circumferences of over 25 meters generally 

 occur as stalagmitic or travertine layers, as they rarely have suffi- 

 cient space to permit them to attain their mature circumference. 



ACKNOWLEDGMENTS 



I wish to thank Dr. Herbert Insley, formerly petrographer for 

 the Pittsburgh Station of the United States Bureau of Mines, and 

 now with the United States Bureau of Standards, at Washington, 

 D.C., for his assistance and suggestions; also Dr. Clark Wissler, 

 curator of anthropology, American Museum of Natural History, 

 New York City, for his assistance in securing access to rather 

 uncommon publications, 



' Ibid., p. 258. 



» Farrington, loc. cit. 



