243 



from the north at various times during- the accumulation of the deposits. 

 The sheets of till found at different depths in the terrace gravels indicate 

 this. The moraine extending along the south side of the Wea Plains as 

 far east as the Little Wea Creek is composed of hills and ridges of gravel, 

 while farther east it becomes a ridge of till. 



This may indicate that after the valley had been filled nearly to its 

 present level the ice swept over it from the north, transpoi-ting the gravel 

 from the valley and depositing it in the moraine. 



The arrangement of the moraines on either side of the river at LaFay- 

 ette, together with the narrowness of the valley at that point, may indicate 

 that the front of the ice sheet lay across the valley while the moraines 

 were deposited. 



The terminal drainage may have spread gravel deposits over the sux*- 

 faee of the Wea Plains much as the Yahtse River is building its delta below 

 its outlet from the IMalaspina Glacier in Alaska. Tliis may have been a 

 line of interlobate drainage between lobes from the Lake Erie and Lake 

 Michigan basins, and much of the material may have been furnished by 

 the slow, liut long-continued creep of the glacier toward the sti'eam 

 line. 



The height of the terraces was determined by the height of the rock 

 surface crossed by the river between the west line of the county and At- 

 tica. The terraced arrangement is continued here, but the upper valley 

 has been made by the removal of the drift from the surface of the rock, 

 while the inner valley has l)een cut tlu-ougli the rock (mainly shales) since 

 the gravel was deposited above. The excavation of the inner valley 

 through Tippecanoe County proceeded as the channel through the rock 

 sill below was cut down. The stream that did this work carried the 

 waters of the melting sheet of ice as it retreated slowly to the north and 

 east. Its width probably corresponded to that of the inner valley. 



Tlie Tippecanoe River and Wild Cat Creek were streams of great vol- 

 ume as the size of their valleys show, and this vohmie was doulitless main- 

 tained through a long period of time. 



The sand dunes southwest of LaFayette along the eastern edge of 

 the Wea Plains Terrace, those on the terrace edge on the north side of the 

 river opposite tlie mouth of Wea Creek, and the deep deposit on the crest 

 of the bluff above the mouth of Indian Creelv were probably gathered and 

 piled up from the surface of the Wea Plains by the southwest 'winds, 

 while, after the recession of the ice, the surface remained bare. 

 14— Academy of Science. 



