Drift of Northwestern loiva. — Bam. 173 
deposit. Except that Wlieatland township seems less eroded 
by its position far from large streams, there is nO' apparent 
evidence in the topography of difference in the age of the 
various parts of the region. Accordingly the two sorts of 
drift are believed to represent but differing phases of the 
Ivansan. The unleached drift resembles closely the Kansau 
usually found five to ten feet below the base of the ferretto. 
[t is as if a portion of the Kansan had been in places eroded; 
and that, in short, is believed to be the correct explanation of 
the phenomena. 
It is obvious that the presence of the lime in the drift de- 
pends upon its original abundance and the degree to which it 
has been carried away. The former is wholly independent 
of the time the drift has been exposed and the latter may or 
may not vary with the time but in the absence of specific evi- 
dence to the contrary may be fairly assumed to be dependent 
on that factor. All the drift sheets of Iowa carry when unal- 
tered, enough lime to make the acid test a valuable one. The 
presence or absence of lime then in the upper portion mav. 
unless good evidence of its exceptional nature be offered, be 
considered to indicate the amount of exposure which the 
drift has suffered. The amount of lime leached from a cal- 
careous drift will depend upon the strength of the solvent and 
the amount passing through the drift in a given time. It 
will also depend upon the direction which the percolating wa- 
ters take. In an arid region the excessive evaporation may 
locally cause the flow of ground water to be upward and lead 
to the deposition of soluble salts in the upper portion of the 
soil. This factor can, however, hardly be important in the 
]3resent case. There is no reason to believe that water soak- 
ing into the ground in one part of Iowa varies greatly in 
solvent power as compared with that in any other part when 
considerable districts are considered. There are of course 
wide differences in detailed areas, but in general the rain 
Avater, which is the original source of the underground circu- 
lation, seems as likely to become charged with hunnis and 
other acids at one point as another. It is true, however, thai 
the amount of water entering the ground varies widelv. There 
are considerable differences in the rain fall in different parts 
<of the state, the variation in 1897 being from 18.43 inciics to 
