150 Wisco7isin Academy of Sciences, Arts, and Letters. 



the opening of vertical fissures. These admit the water from 

 below, and by the freezing of that water they are filled, so that 

 when expansion follows a subsequent rise of temperature, the 

 ice cannot assume its original position. It consequently in- 

 creases its total area and exerts a second thrust upon the shore. 

 Where the shore is abrupt, the ice itself yields, either by crush- 

 ing at the margin or by the formation of anticlinals elsewhere ; 

 but if the shore is generally shelving, the margin of the ice is 

 forced up the acclivity, and carries with it any boulders or other 

 loose material about which it mav have frozen. A second lower- 

 ing of temperature does not withdraw the protruded ice margin, 

 but initiates other cracks and leads to a repetition of the shore- 

 ward thrust. The process is repeated from time to time during 

 the winter, but ceases with the melting of the ice in the spring." 



This explanation is the best and most satisfactory of any I 

 have yet read. However, the observations made during the last 

 two seasons have added a number of interesting details, espe- 

 cially concerning the manner in which the ice behaves while pro- 

 ducing these striking shore phenomena, which it may be profit- 

 able to discuss in the succeeding pages. 



The entire phenomenon of ice ramparts depends upon the ex- 

 pansion and contraction of the ice sheet resulting from abnor- 

 mal fluctuations in the temperature of the ice. The deforma- 

 tion of the ice sheet itself is a much more complicated story than 

 the formation of the ice rampart. The ramparts which form 

 along the shore are only the more striking manifestations of the 

 forces resulting from changes in the temperature of the ice. 

 They occur only under exceptionally favorable conditions, while 

 the deformation of the ice sheet as a result of the same agency 

 occurs each winter. 



At a temperature of 39° F. water is at its maximum density. 

 An increase or decrease in its temperature results in expansion. 

 When the temperature of water is lowered to 32° F. it solidifies, 

 and if free to move, linear contraction sets in at the rate of about 

 Toooofor each degree centigrade org^eooofor each degree Fahren- 

 heit.^ If the ice is not free to move the tensile stresses will ac- 



' As determined by Struve, the linear coefficient of expansion is .000053 for each de- 

 gree centigrade.— See Pogrgendorffs Annalen ; Vol. 66, p. 298. Edward S, Nichols ob- 

 tained nearly the same result. See Phys. Rev. Vol. 8, pp. 184-186. 



