ABSTRACT OF VOLUME. XIX 



culmination of the Wisconsin stage. It may also be inferred by a change in the atti- 

 tude of the laud, by which better drainage conditions were prevalent in the Wisconsin 

 than in the Iowan stage. 



Chapter IX. The early Wisconsin drift sheets. — The Wisconsin drift, 

 named by Chamberlin from the State in which it was first recognized as a distinct 

 drift, is characterized by large morainic ridges and comparatively smooth intervening 

 till plains which have been thrown into two groups, known as the early Wisconsiu 

 and late Wisconsin. In the first group the moraines form a rudely concentric scries, 

 which are well displayed in the northeastern part of Illinois, but are largely over- 

 ridden by the moraines and drift sheets of the later group in districts farther east. 

 The outer border of the second, or late, Wisconsin group is so discordant with the 

 moraines of the first group that there seems in this feature alone sufficient reason for 

 separation. 



The several morainic systems of the early Wisconsin group are taken up in suc- 

 cession from earlier to later, the distribution, relief, range in altitude, surface contours, 

 thickness and structure of the drift, and the character of the outwash being con- 

 sidered. In connection with each morainic system the associated till plains are 

 discussed, attention being given to. the surface features and to the structure and 

 thickness of the drift. In northern Illinois the several morainic systems are merged 

 into a composite belt so complex that it is difficult to trace the individual members 

 The several moraines and their associated sheets of till do not appear to be 

 separated by intervals so wide as are found between the Illinoian and Iowan or the 

 Iowan and Wisconsin drift sheets. Indeed, instances of the occurrence of a soil or a 

 weathered zone between Wisconsin sheets are very rare. There may, however, have 

 been considerable oscillation of the ice margin. 



Chapter X. The late Wisconsin drift sheets.— The basis for separation 

 from the early Wisconsin is first considered, after which the several morainic systems 

 and their associated till plains are taken up in order as in the discussion of the early 

 Wisconsin drift. An interpretation of the Kankakee sand area is attempted, though 

 several questions connected with it still remain open. The chapter closes with a 

 discussion of the striai found within the limits both of the early and of the late Wis- 

 consin drift. 



Chapter XL The Chicago Outlet and beaches of Lake Chicago. — That 

 a body of water once extended over the low districts bordering the southern end of 

 Lake Michigan and discharged southwestward to the l)es Plaines and thence into 

 the Illinois Eiver has been recognized since the early days of settlement, and several 

 papers discussing the beaches and the outlet have appeared. The latter has long 

 been known as the Chicago Outlet, because it led away from the site of that city. 

 The lake has recently been given a name in harmony with that of the outlet (Lake 

 Chicago.) 



