REVIEWS 365 
advisable to apply the name Peorian, while the relations of the Toronto 
formation remain uncertain, Other exposures as well as those near Peoria 
are discussed. A marked interglacial interval between the Iowan and Wis- 
consin stages of glaciation may also be inferred by a comparison of the 
outline of the ice sheet at the Iowan stage of glaciation with that of the out- 
line at the culmination of the Wisconsin stage. It may also be inferred by 
a change in the attitude of the land, by which better drainage conditions were 
prevalent in the Wisconsin than in the lowan 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 dis- 
tinct drift, is characterized by large morainic ridges and comparatively smooth 
intervening till plains which have been thrown into two groups, known as the 
early Wisconsin and late Wisconsin. In the first group the moraines form a 
rudely concentric series, which are well displayed in the northeastern part of 
Illinois, but are largely overridden 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 succession 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 considered. 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 I[]linois 
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 I]linoian 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 dis- 
cussion 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 striz found within the 
limits both of the early and of the late Wisconsin drift. 
Chapter XT. 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 Des Plaines and 
thence into the Illinois River has been recognized since the early days of 
