140 WALTER LOUIS HAHN. 



single chain of subterranean passages with five openings. These 

 passages are merely a single underground waterway with a good 

 sized brook covering the floor in most places. At two points 

 the roof has fallen in leaving sections of the stream bed exposed. 



^-H3 '"'" " " ■ " * 



Fig. I. /, Entrance to Shawnee Cave ; 2, lower chamber ; j, blind passage ; 4, 

 large chamber ; 5, entrance to Lower Twin Cave ; 6, entrance to Upper Twin Cave ; 

 7, entrance to Lower Spring Cave ; <?, entrance to Upper Spring Cave. Arrows show 

 direction of stream. 



These openings have been named as separate caves. The size va- 

 ries considerably, but the average height is, perhaps, six feet and 

 the width ten. In some places it becomes much smaller and the 

 entire passage is filled with water after a heavy rainfall. In other 

 places the size is much greater, in the large chamber (Fig. i, ^) 

 the distance from water level to the top of the chamber is about 

 40 feet and the width at the widest point about 100 feet. There 

 are numerous lateral passages varying in width from a few inches 

 to several feet. A second large chamber is situated near the 

 extreme lower end of the cave (Fig. i, 2). 



Temperature records kept for a period of two years, in the 

 large chamber at ^, show an extreme variation from about 51° 

 F. in January, to 57° in September. The air at this point al- 

 ways contains moisture nearly to the point of saturation. Baro- 

 metic pressure here varies approximately with the surface pres- 

 sure although the changes take place more slowly. The physi- 

 cal environment of the cave-dwelling bats during their periods 

 of inactivity, is, therefore, nearly constant for all seasons. 



Not less than five hundred bats, representing five species, spent 

 the winter of 1906-7 in these caves. Probably the number was 

 much larger, as only those actually seen were counted and some 

 creep away into the smaller fissures where they cannot be found. 

 These bats come out of the cave to secure food only in twilight or 

 darkness in mild weather. 



Since the temperature is relatively constant in the cave through- 

 out the year and there is always total absence of light, the 

 problem which first presented itself was to determine how the 



