conditions and the place has fallen to the willow. Hence it is^ 

 now generally recognized that a line of willows in natural sur- 

 roundings, indicates a former water line even though there is- 

 no beach-line in evidence. 



Extending through the mesophytic forests on the low 

 ground about the lake and especially upon the southern and 

 eastern sides, are numerous lines, in some cases double. 

 These lines are those made by willow trees. Between these 

 lines of trees there is an intervening space of about twenty-five 

 feet. The lines are made up of fully matured Salix nigra. These 

 lines are so peculiarly continuous that they seem to- 

 indicate the former margin of drainage channels. These lines 

 representing tributaries, have in the last century, occupied) 

 many different channels. The streams have wandered at will 

 over old lake bottoms, whence the lake water has receded, so- 

 that'they represent typical flood-plains. It is on these prim- 

 itive flood-plains that Salix nigra grows in such continuous 

 lines, suggesting the history, at least in part, of the creek and 

 lake. In one small area especially studied, six different oscil- 

 lations of the channel were observed. In some cases the evi- 

 dence of ecology was corroborated by the still lingering de- 

 pressions or extinct channels in the ground. 



THE ANCIENT LAKE 



About one-fourth mile to the east of Chicago and Hamil- 

 ton Hills, the two eskers mentioned near the Biological stat- 

 ion, one comes suddenly upon aMarge and continuous embay - 

 ment. It is now dry having no water connection with the 

 lake. Formerly it was filled with an arm of the old lake. 

 Now it has the appearance of a deep and wide valley. Hid- 

 den from view by heavy forest growth, the valley appears as a 

 case of past erosion at a time when an enormous amount ot 

 water went through it. It is impossible to suppose that the 

 present feeble stream which meanders through the deepest 

 parts was ever competent to perform any such amount of ero- 

 sive work. It seems like placing the Tippecanoe River in the 

 valley of the Mississippi and making it responsible for the 

 valley. The idea, then, that this great embayment was the 

 result of erosion, is clearly unsatisfactory. Neither is it prob- 

 able that the valley is one formed by river erosion but one evi- 



12 



