Buchley — Ice Ramparts. 157 



2nd condition. — Lake covered with the ice sheet and tem- 

 peratnre still falling. Kesult : — Ice thickens below, raising up- 

 per surface. Tensile stresses are set up, on account of which 

 cracks form at surface. The openings thus made penetrate 

 through the thickness of the ice and thej are filled with water 

 from below, which soon freezes. The cracks open repeatedly 

 until the temperature reaches its lowest point. The ice sheet 

 is then approximately adjusted, at the minimum temperature, 

 to the size of the lake basin. 



3rd condition. — Temperature of ice rises. Kesult: — Com- 

 pressive stresses are set up, which cause the ice to expand. The 



relief comes either through the formation of ridges in the ice 

 sheet, or the formation of ice ramparts along the shore. Cracks 

 also form from the under surface of the ice. 



4th condition. — Free-zing temperature. Result. — Water wells 

 up into the cracks and freezes. Ice sheet becomes a solid 

 mass as before approximately adjusted to the size of the basin. 



This completes the cycle of changes in the ice due to varia- 

 tions of temperature. 



Madison J ^Yis.J January, 1900. 



