118 



IOWA ACADEMY OF SCIENCE 



Vol. XXVI, 1919 



Figure 16 shows the lower end of one of the upper pools in this 

 stretch. The banks on either side of the stream here are higher and 

 in at least three places springs enter the stream from these banks. 



Fio. 18. — Same sink hole as seen in Figure 17 after a heavy rain. 



Fig. 19. — Water flowing into uppermost ciuarry after a heavy summer rain. 



The springs are not, however, well defined. Beginning at Station 6 

 a very interesting thing happens. From here on the bed of the 

 stream is limestone. At Station 6 the stream disappears completely 



