REVIEWS 367 
Chapter XIV. The wells of Illinois —This chapter aims to present all 
the reliable well records obtained within the state which throw light upon 
the deposits penetrated, as well as upon the character of the water supplies. 
In addition to the wells which terminate in the drift, there are included many 
which extend deeply into the underlying rock formations. This necessitates 
a classification of the underground waters and a description of the several 
rock formations penetrated, including a discussion of the attitude of the 
strata. The essential conditions for obtaining artesian wells are considered, 
and also the relation of the drift to the ordinary wells. There is a brief 
discussion of gas wells, confined mainly to those obtained in the drift. A 
tabulation of sources for city water supply is then presented, after which there 
appears a detailed discussion of wells, taken up by counties. 
Chapter XV.  Soils——The sources of soil material are first discussed. 
_An attempt is then made to classify the soils according to their origin. Eight 
classes are recognized as follows: Residuary soils, bowlder clays, soils, grav- 
elly soils, sandy soils, bluff-loess soils, silts slowly pervious to water, fine silts 
nearly impervious, peaty or organic soils. 
The matters of chief general interest will doubtless be found in the 
classification of the glacial series, in the changing configuration of the 
ice at its successive stages, in the differences of the deposits at the 
different stages, and in the estimate of the average thickness of the 
drift. 
In the matter of classification, the monograph presents the latest 
and fullest expression of the conclusions toward which investigations 
in the interior have been steadily tending for the past decade. The 
classification offered is not regarded as final, either in the sense of 
including all the possible great divisions, or in the complete charac- 
terization of those recognized, but it clearly lies in the line of a true 
and ultimate classification. Fifteen stages are recognized, six of which 
are based upon notable glacial advances, five represent notable inter- 
vals of deglaciation, and four are based upon lacustrine stages after 
the beginning of the abandonment of the region by the last ice-sheet. 
The age of the oldest glacial formation is regarded as many times 
that of the latest ; and the oldest interglacial intervals are also believed 
to be many times longer than the later ones. In a word, the oscilla- 
tions appear to have been large in the earlier stages and to have 
grown less and less during the progress of the period. This newer 
view of the relative ages of the successive epochs, sustained as it 
appears to be by the progress of research in Europe, must be looked 
upon as one ofthe most important advances of recent years, for 
