GEOLOGIC CORRELATION 
251 
south, can be suggested for Iowa, where the rocks are mainly 
known only from the records of deep-well sections. 
Of the Ozarkian series the Jefferson dolomite appears to be 
very nearly the exact equivalent of the Shakopee dolomite of the 
north. The Roubidoux sandstone corresponds to the New Rich- 
mond sandstone of the same region. The G-asconade dolomite 
probably represents somewhat more than the Oneota dolomite. 
The Gunter sandstone is a local deposit. 
In the Ordovicic division the Early part of the sequence, 
represented by the Yellville dolomite, does not appear to be 
found in the north. Early Siluric sedimentation is not repre- 
sented in Iowa by deposits. Early and Mid Devonic terranes, 
which have no sedimentative representatives in Iowa, are well 
developed in the south. 
The Tennessean series, which is so poorly developed in Iowa, 
reaches in southern Missouri a quite remarkable thickness and 
attains great diversity in lithologic character. In its geographic 
distribution it extends far southeastward into Alabama; while 
the Mississippian series extends southwestward. The two series 
therefore, really belong to quite distinct geographic provinces, 
the sedimentation of which overlaps somewhat along one edge. 
The importance of this distinction is not generally recognized. 
The Arkansan series in both Missouri and Iowa is represented 
by a marked hiatus. The plane of unconformity bevels all older 
strata in such a manner as to indicate a long period of erosion, 
if .not one of complete planation. On the south side of the 
Ozark dome in southern Missouri appears the feather-edge of the 
great Arkansan formation comprising coal-bearing shales and 
sandstones. This attains in central Arkansas an enormous thick- 
ness of more than 15,000 feet. This series is the depositional 
equivalent of the unconformity which characterizes the base of 
the coal measures in both Missouri and Iowa. The entire Car- 
bonic succession appears so important terranally and has so 
many marked division lines that Chamberlin and Salisbury, pro- 
pose to assign a taxonomic rank to each of its two principal di- 
visions equivalent to that of Devonic or Cambric. This pro- 
cedure is not believed to have sound stratigraphic foundation; 
and it is difficult to see how the proposal is any distinct ad- 
vance over our prior conceptions. 
Another notable difference between the Missouri and Iowa 
general sections is the presence in the first named state of ma- 
rine Tertiaric beds; and in the last mentioned state of conti- 
nental deposits of the same age. The correlation of both of these 
sections with the great Southwest standard section is also given. 
