from the bottom. The greatest depth, 116 feet, was reached in 

 these operations northwest from Ft. Dodge Point, and on a line 

 drawn from the Inn to Pillsbury's Point. A depth of over 100 

 feet was also reached a little south of west of Pillsbury's Point. ^ 

 The greater part of the deeper portion of the lake, extending 

 from opposite the lower portion of Emerson's Bay to a point op- 

 posite Manhattan Beach, varies from 60 to 80 feet in depth. The 

 deepest portion of Emerson's Bay is about 35 feet; of IVIiller's 

 Bay 35 feet; of the upper portion of the lake above Manhattan 

 Beach 40 to 60 feet ; and of the bay opposite Arnold 's Park about 

 30 feet. Emerson's Bay is cut off from the main body of the 

 lake by submerged reefs, thus forming practically an enclosed 

 basin. This is also true of the bay north of Arnold's Park 

 which is cut off by submerged reefs extending out from Ft. 

 Dodge Point, and Pillsbury's Point. Lliller's Bay is similarly 

 partly cut off. These enclosed basins are very rich in vegeta- 

 tion, and furnish exceptional opportunities for the study of the 

 aquatic flora of the lake. The inner portion of Miller's Bay, on 

 the north side, opposite the Laboratory, offers the richest field for 

 such study in all the region under discussion. 



The lake border everywhere presents a greater or lesser abun- 

 dance of aquatic vegetation and at many points offers excellent 

 opportunities for zonal studies, the more conspicuous green vege- 

 tation extending to a depth of 30 to 35 feet. Beyond this depth 

 diatoms are abundant, especially in the soft, brownish ooze 

 which covers the bottom of the deeper portions of the lake to a 

 depth of several feet. Excellent opportunities are also offered 

 for plankton studies in this and other lakes, — a field as yet al- 

 most untouched in this region. 



Center lake is the largest of the smaller lakes, and lies between 

 the two Okoboji lakes. Again the groves represented on the map 

 mark the position of steep banks along the margin of the lake, 

 with bowldery banks as before, or, as on the south side of the 

 lake, the surface is rough and rolling. A part of the sandy 

 beach, illustrating the effect of ''ice-shove," on the southeast 

 shore, is shown in Plate VI, fig. 3. The hills on the southwest 

 side rise to a height of more than 30 feet above the lake, and the 



3 The greatest depths in the lake, recorded in Bulletin no. 32 of the Engineering 

 Experiment Station of the Iowa State College of Agriculture and Mechanic Arts, 1913, 

 are 132 feet nearly west of Ft. Dodge Point, and 124 feet north of west of Pills- 

 bury's Point. 



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