270 The American Geoloijist. Aiu-ii, 1897 
that lakes are known at present where the drainage is through 
more than one channel, and each one has been absolutely 
formed b}'' natural processs, since they lie within the domain 
of an uninhabited region. 
The opponents to the dual drainage lake existence have 
combatted more upon theoretical than practical grounds, since 
they insist that it is contrary to all known physiographic 
principles for, a lake to exist with more than one natural out- 
let, for any length of time. For, given the two outlets, con- 
ditions will favor the one more than the other for lowering 
its channel, and just as soon as the one has reached a certain 
stage in erosion, this will form the permanent overflow, and 
the other will be abandoned. Theoretically this is true, but 
there are other considerations and some instances most as- 
suredly prove that conditions are favorable and have been so, 
for the drainage of a lake through more than one channel at 
the same time. 
EDITORIAL COMMENT. 
Synopsis of the Drift Deposits of Iowa.* 
Studies pursued with the object of determining the distri- 
bution of certain types of soil and their relations to the drift 
sheets covering the state have incidentally demonstrated that 
the succession of Pleistocene deposits is more complete and 
more clearly indicated in Iowa than in any other correspond- 
ing area of this continent so far studied. The margin of the 
Wisconsin drift sheet was traced some j'-ears ago by Upham, 
but until recently this was the only Pleistocene deposit whose 
boundaries were approximately known. Two sheets of till 
were differentiated by McGee in northeastern Iowa, but it re- 
mained for the present survey during the past two years to 
recognize the southern limits of McGee's upper till. Mr. Bain 
has pointed out a body of drift below McGee's lower till, and 
sharply ditferentiated from it, and Mr. Leverett of the U. S. 
Geological Survey, has demonstrated the existence of drift in 
southeastern Iowa, intermediate in age, between the lower and 
upper till of McGee. The Pleistocene history of Iowa as now 
*From the Administrative report of the State Geologist of Iowa for 
1896. 
