250 
IOWA ACAD53:MY of scieince 
Texas, New Mexico and Arizona will be presented, as parts of a 
broad but exact scheme of general correlation. 
As fundamental elements in the upbuilding of the North 
American continent the areas of Iowa and Missouri present some 
exceptionally instructive contrasts. In the geological sections 
of these two states the record of each physical event is accentu- 
ated and paralleled with those of others. 
Several notable features first deserve enumeration. In the 
one area certain phases of unconformity are represented by tre- 
mendous sections of sediments. At one time a great and lofty 
mountain range stretched across the northern area, while in the 
south remained a lowland plain. In its present aspect the Ozark 
dome did not exist until very recent times. These circumstances 
have an important bearing upon the proper interpretation of the 
regional stratigraphy. 
For many years the two sections have appeared to be , so un- 
like that little exact comparison was possible. This apparent 
discrepancy arises from several causes. First, there is small 
attempt to assign to the several geologic formations recognized 
their proper taxonomic ranks. Second, different names for the 
same terranes are used in the two states. Third, state lines pre- 
vent workers in the one province from extending their investi- 
gations into adjoining districts and thus making exact strati- 
graphic correlations. Fourth, terranes are represented in one 
state which have no exact depositional equivalent in another. 
Fifth, change in lithologic character of formations tend to con- 
fuse the delimitation of formations. 
The similarities of the two sections are as important as are 
their differences. The former are the more apparent since the 
taxonomic values of the several formations, the usage of the 
same nomenclature, and the positions of the terranes in the time- 
scale are made to harmonize in a way never before attempted. 
To the detailed differences attention is specifically called in an- 
other place. 
Of the larger differences between the two sections the most 
notable may be briefiy enumerated. First of these are those 
which relate to the Cambric rocks. The Croixan series, which 
in Iowa is scarcely exposed above stream-level, is well differen- 
tiated in Missouri and widely outcrops around the Ozark dome. 
Although the successions in the two states have nearly the same 
thickness no equivalents of the subdivisions recognized in the 
