IOWA ACADEMY OF SCIENCES. 51 



East Okoboji Lake is composed of three small lakes in a 

 chain, the water varying from three feet in the upper one to 

 eighteen or twenty feet in the lower one. The deposit varies 

 also from eight feet in the upper to a much greater depth in 

 the lower. Here there is a much greater percentage of sand 

 than in Clear Lake, due to more extended surface drainage 

 and steeper hills. 



The channel, however, which connects East Okiboji and 

 West Okiboji Lakes, is the most remarkable place of all. 

 Remarkable, not only for the number of diatoms, but for a 

 host of other aquatic forms growing in the most lavish pro- 

 fusion. The conditions here are certainly very favorable for 

 plant growth. High hills, covered with trees, protect the 

 channel from the winds, and its form precludes the possibility 

 of large waves. Then, too, a gentle current sets from one 

 lake to the other, keeping the water in fine condition. In the 

 fall, after the larger plants have passed their perfection and 

 have begun to die, the diatoms overrun them all and, indeed, 

 every other thing below the surface of the water. The com- 

 mon bladderwort becomes the home of vast colonies of the 

 stalked forms, as cocconema, gonphonema, bands of fragil- 

 laria, with long, acicular synedra intermingled. Acres are 

 thus covered, where there are no large waves and the water is 

 not too deep. In those parts of the lake where rushes grow, 

 each one is covered below the water line with a layer a half an 

 inch or more in thickness. 



Across this channel a railroad was built, and in so doing a 

 diatomaceous deposit was found fifty-two feet deep 



In West Okiboji Lake water was found 125 feet deep, the 

 deposit being of unknown depth. So soft and yielding is this 

 material that a dredge, weighing only two or three pounds, 

 when dragged along the bottom sinks into it to a depth of ten 

 or twelve feet. 



In comparing the species found here with those found in 

 Clear Lake, both lying in the same geological formation and 

 no great distance apart, it is seen at a glance that they are 

 utterly different. In Clear Lake such genera as suriraya, 

 navicula, cymbella, eunotia pleurosigma and cymatopleura 

 are found, as compared with cocconema, odontidium, stictodis- 

 cus and synedra in Okoboji Lake. 



Silver Lake also adds a small quota, but has not been care- 

 fully examined. 



