226 



for by the action of the ice subsequent to the time when the marsh was left with- 

 out water. Some of the most striking examples of ice action in the formation of 

 beaches are found along the east side of Johnson's Bay; along Crow's Bay; at 

 Morrison's Island, where two ice beaches, separated by a few feet, are now cov- 

 ered by trees; at Clark's Point, where an old beach extending as much as 200 

 feet from shore is found, and at Black Stump Point. 



CHARACTER OF BOTTOM. 



In the shallower parts of the lake the bottom is composed of sand, gravel, 

 and small boulders, except along the low marshy shores, where it is composed of 

 mud. At several places, both in Syracuse Lake and in the main lake, dredgings 

 were taken at depths from 25 feet to 60 feet. Here the bottom was covered with 

 a deposit of marl in which were found many diatoms and shells. 



Further investigations will be carried on to determine more fully the charac- 

 ter of bottom at different depths. 



For information concerning the freezing of the lake I am indebted to Mr. J. 

 P. Dolan, who has given me the history of ice formations as he has observed them 

 during years past, and he has furnished me with records of careful observations 

 made since the first formation of ice in October, 1895. These observations, unless 

 otherwise indicated, are for Syracuse Lake. Ice forms on the main lake at the 

 same time, but it does not freeze entirely over so soon as Syracuse Lake. 



The lake begins to freeze along the edge, except where strong springs enter 

 near the margin. Information has been obtained concerning the influence of 

 springs only at Crow's Baj' and Vawter Park. Springs are numerous along 

 Crow's Bay for a half mile and the water along the edge is kept open after the 

 lake is frozen over, but I have not yet learned to what extent these springs in- 

 fluence the freezing of the edge of the lake in this locality. From Mr. Smith 

 Vawter, who has observed the springs at Vawter Park for a number of years, I 

 learned that the spring, which is near the margin of the lake and 200 feet east of 

 the Biological Laboratory, keeps the edge of the lake open throughout the w^inter. 

 If the weather is not severe, ice does not form for 25 feet along the shore, and 

 from 12 feet to 15 feet from shore. In the severest weather the lake is kept open 

 for 2 or 3 feet from the margin. 



The ice spreads rapidly from the shore towards the center. The lake freezes 

 ove*- quite rapidly when the general temperature remains below 32° Fahrenheit 



