THE GROWTH OF STALAGMITES AND STALACTITES 117 



Poor evaporation and high concentration (or both) mean that 

 the spattering drops will eventually form a small mound ' which 

 will increase in height and decrease in diameter until the drip and 

 evaporation surface is in equiUbrium. It will then grow sym- 

 metrically, in a vertical direction, unless conditions change (Fig. 15). 



Rapid growing stalagmites 



/St. stage 2nd. stage 3rd stage 4th. stage 



Slow growing stalagmites 



Fig. 15. — Diagrammatic sketch of method of growth of stalagmites 



UNSYMMETRICAL STALAGMITES 



A "mushroom" stalagmite is one in which the diameter has 

 increased after a period of small diameter growth. 



A "stool" stalagmite is a "mushroom" stalagmite in which 

 the diameter has returned to about the same original diameter 

 after the "mushroom" enlargement, 



A "needle " stalagmite is one in which the diameter has decreased 

 after a period of large diameter growth. 



A "choked" stalagmite is one in which the diameter has returned 

 to about the same original diameter after the "needle" effect had 

 taken place. 



The "mushroom" effect is caused either by an increase in the 

 drip or a decrease in the conditions of evaporation. In the case of 

 an increased drip, the slope between the original diameter and the 

 enlarged diameter will be gentle because the vertical growth will 

 increase slightly at the same time that the diameter increases. 

 In the case of decreased conditions of evaporation, the slope between 

 the original diameter and the enlarged diameter will be abrupt 

 because the vertical growth will be decreased at the same time 

 that the diameter is increased. If the original conditions return 



