THE PLANKTON OF SHAWNEE CAVE. 



391 



flood. This may be due to the influence of the residual water in 

 the cave (see Table I.). 



TABLE I. 



SHOWING THE RELATION OF FLOOD TO TEMPERATURE OF CAVE WATER. 



Winter. 



Summer. 



Air Currents. The air in the cave is in almost constant motion. 

 In general it flows up during the winter and down during the 

 summer months. However, during the spring and autumn, the 

 current reverses several times before the constant direction of the 

 extreme season following is assumed. The direction of the cur- 

 rent was down on October 14, and reversed on October 21, 22, 

 23, 26 and 30. After December 10 the air moved upward until 

 the unstable period of spring began, which occurred about the 

 end of March. 



The rate of the current varies in different parts of the cave, 

 being scarcely perceptible in the large rooms and very marked 

 where the cave is small in cross-section. Observations taken at 

 a single point indicate that the rate of the air current varies 

 directly with the divergence of the subterranean and surface tem- 

 peratures. Rate of air currents was measured with a meter re- 

 cording a minimum of 30 feet per minute. 



The upward moving current of cold air weathers the rocks in 

 the regions of the lower openings of the cave, giving them in 

 general a funnel shape. In this enlarged region there is always 

 an upper stratum of air moving in the direction opposite to that 

 of the primary cave air current. 



The closed passages near Shawnee entrance have the ordinary 



