DRIFT PHENOMENA IN WISCONSIN 



143 



example of a glacial lake which became extinct by having its basin 



filled during glacial times, by sediments washed out from the ice. 



Near the northwest corner of this flat, an exposure in the 



sediments of the old lake bed shows the curiously contorted 





-J^4 



'.y 



Fig. 6. Contorted layers of sand and silt, in the bed of the extinct glacial lake. 



layers of sand, silt, and clay represented in Fig. 6. The layers 

 shown in the figure are but a few feet below the level of the flat 

 which marks the site of the lake. It will be seen that the con- 

 torted layers are between two series of horizontal ones. The 

 material throughout the section is made up of fine-grained sands 

 and clays, well assorted. That these particular layers should 

 have been so much disturbed, while those below and above 

 remained horizontal, is strange enough. The grounding of an 

 iceberg on the surface before the overlying layers were depos- 

 ited, or the action of lake ice may have been responsible for the 

 singular phenomenon. 



