BIOLOGY OF PHYSA 19 



of the lake in which the fish spawn. The water is clear and the 

 substratum is of a fine texture, due to the formation of peat, 

 so that it is not unusual to see the snails crawling upon the 

 submerged roots and stems of the sedges instead of on the more 

 unstable substratum. 



The conditions making up this habitat are as follows: Fairly- 

 shallow water; unshaded, except by tall sedges; few water 

 weeds (algae and Riccia) ; protected from wave action ; fairly- 

 free exchange of water from the lake; very oozy substratum 

 and probably numerous enemies. 



d. Habitats Behind Spit and Bar Formations. Crooked Lake 

 is about one mile west of Kavanaugh Lake and resembles it 

 in size and general setting in that it has the same type of sur- 

 rounding morainic hills, and gravelly bottom and shores. The 

 chief point of difference between the two lakes is in their shape 

 and in the consequent forces at work modifying their contours. 

 Crooked Lake, in general outline, is not alone crooked, as its 

 name rightly implies, but possesses also many minor irregu- 

 larities which form small bayous which are being cut oft' from 

 the main waters by various stages of spit and bar formation.^ 

 In fact, the general tendency of the lake seems to be that of 

 rounding out its ragged outline. Bars are being formed both 

 by currents and wave; erosion is going on on the north and 

 west shores, and debris is being carried and built into spits 

 and bars upon the south and eastern portions of the lake. The 

 currents fail to conform to the curve of the shore and leap from 

 point to point of land, thus cutting across the small bays. By 

 the deposition from currents at their free ends spits are being 

 extended and this growth goes on until each spit completely cuts 

 off a portion of the lake and allows it to live out the shorter 

 life of a pond or pool. The past work of the lake is shown by 

 several small lagoons which have been cut off from the lake by 

 bars and which now form part of the beach. 



The following changes are taking place in the lake which are 

 certain in the future to alter the present shores, and in con- 

 sequence affect the life in its waters: 



I. The north and west shores are being cut away and in con- 

 sequence will become steeper while the south and east 

 shores are being built out into the water. 



^cf. Gilbert, The Topographic Features of Lake Shores (1885). 



