PRAIRIE SYNCLINORIUM 
271 
mountain building. Both the latter and the production of the 
great synclinorium belong to Early Cretacie, or Comanchan 
time. 
The later physiographic features of the region are also not 
without great interest. With the planing down of the moun- 
tains and the peneplanation of the entire region in Comanchan 
times the Mid Cretacie deposits were laid down over the old 
land area not only where they are found outcropping today, in 
northwestern Iowa and southeastern Missouri but they doubtless 
once extended unbrokenly over the whole country intervening. 
This surmise is substantiated by the recent discovery, in Mercer 
county, Missouri, far beyond the southernmost known exten- 
sion of the Nishnabotana sandstone in Iowa, of undoubted ledges 
of typical Dakotan sandrock. 
Below the floor of the Cretacie formation, the Comanchan 
baselevel, more than 2,000 feet of Late Carbonic sediments ap- 
pear to have been removed from the Iowa area. This section^ 
includes besides about 200 feet of the Missourian series, 700 
feet of the Oklahoman series, and 1,000 feet of the Cimarronian 
series. 
To the downward bending of the rocks in the great tract be- 
tween the Siouan and Ozark mountain regions we owe the pres- 
ervation of our vast stores of mineral fuel. Were it not for 
this circumstance we would not have within the borders of our 
state a single workable deposit of coal. Our entire common- 
wealth would be as barren of coal as now are northeastern Iowa, 
northern Illinois, Wisconsin and Michigan — ^vast areas over 
which the productive coal measures without question originally 
extended, but which were removed during the prodigious de- 
nudation which took place over all this region during Comanchan 
times. 
