144 Wisconsin Academy of Sciences, Arts, and Letters. 



During the periods of low temperature the ice increased in 

 thickness until it attained a maximum of from thirty to forty 

 inches. Shallow portions of the lakes were frozen to the bot- 

 tom, and in many of the especially shallow places the bottoms 

 of the lakes were frozen beneath the ice. 



Turning our attention from the conditions prevailing at that 

 time to the resultant shore phenomena, we distinguish three dif- 

 ferent forms of ice ramparts, which depend for their peculiari- 

 ties largely upon the size, shape, and composition of the bank. 

 The first kind occurs along a sand or gravel beach of gradual 

 slope; the second kind occurs along an abrupt shore, adjacent to 

 which the water is somewhat deep ; and the third kind forms at 

 the head of bays where the shore is low, marshy meadow-land, 

 adjacent to which the bottom of the lake is composed of mud, 

 marl, and weeds. There are all gradations between these forms. 



Examples of the first kind were observed at many favorable 

 places along the shore of both Mendota and Monona. In many 

 of the especially shallow places, as stated above, the bottom of 

 the lakes had frozen to a considerable depth below the water. 

 During the periods of expansion the frozen lake bottom, consist- 

 ing of boulders, pebbles, and sand, together with the ice sheet 

 above, to which it was welded, was shoved up the gradual incline 

 of the beach. The boulders, pebbles, and sand composing the 

 lake bottom maintained the same relative positions which they 

 had before they were moved, and when the ice melted later in 

 the season the boulders, pebbles, and sand were left as a thin 

 mantle, often extending six or eight feet beyond and above the 

 edge of the water, (See Plate 11.) The best example of this 

 phenomenon was observed along the beach an eighth of a mile 

 east of the Mendota Hospital for the Insane. (See A, Plate I.) 

 The same was also observed along the southeast side of Picnic 

 Point (See B, Plate I), and at one or two places along the south 

 shore of Lake Monona. (See C, Plate I.) 



The second form of the ice rampart occurred where the shore 

 line was abrupt, forming steep banks of variable height. The 

 result of the ice shoving against such banks depends upon the 

 thickness of the ice and the character and composition of the 

 shore. In some places the bank was uninjured by the ice-shove, 

 relief taking place by the breaking up of the ice near or at some 



