10 



IOWA STUDIES IN NATURAL HISTORY 



great as that of Okoboji ; the 20-25 m. stratum is more than 



three times as thick; the thickness of the 25-30 m. stratum 



is five times, and that of the 30-35 m. stratum ten times as 



great as are the corresponding figures for Okoboji. The 



effect of this difference on temperatures is that the lower 



water of Okoboji lake has a higher temperature and a less 



quantity of heat than would be the case in the lake basin of 



ordinary form. 



II— TEMPERATURES 



TABLE 7— TEMPERATURE OBSERVATIONS ON OKOBOJI LAKE, 

 1919 



* 23.5 m. 



Series No. 1 was taken in the mouth of Miller's Bay. 

 Series No. II near the deepest water, which could not be placed on 

 that day. 



Series No. Ill in deepest water found. 



In the evening of July 29 the hot weather was broken by 

 squalls with rain and the wind shifted to the north, return- 

 ing to south on July 30 and 31. The weather continued cool 

 and the surface temperature fell, while that at 5 m. and 10 

 m. rose. The computations are based on the observations of 



