ACE OF GYPSUM OF CENTRAL IOWA 725 



beds" includes the gypsum, red shales, and sandstone which 

 often overlie it, and three or four feet of fine clay which com- 

 monly occur at its base. Two sections may be given to illustrate 

 their stratigraphic relationships. 



The exposure at what was formerly known as Kohle's Brewery 

 near the mouth of Soldier Creek and within the Fort Dodge city 

 limits has long been regarded as typical for the gypsum and 

 associated red shales and sandstone. 



Feet 



9. Gravel, fresh, clean, well water-worn, containing much limestone - 5 



8. Drift, slightly oxidized, unleached ------ 28 



7. Gravel, rusted, many decayed fragments, showing only at certain 



points along bluff --------- 2 



6. Sandstone, soft, friable, buff-colored, though at points not far away 



it is white and heavily bedded ------- 5 



5, Shales, argillaceous, sandy layers alternating - - - - 5 



4. Sandstone, buff, friable -------- 2 



3. Shale, gray .--_-..-.. 2 



2. Thin bands of gypsum and shale ------ 7 



1. Gypsum, massive, exposed - - - - - - - - 11 



SECTION IN THE PIT OF THE FORT DODGE CLAY WORKS. 



3. Drift, yellow, unleached, lower part a little darker than the upper 35 



2. Red sandy shale, with occasional thin bands of sandstone - - o-io 

 I. Gray Coal-Measure shales, often containing fossils of ferns, lepido- 



dendrons. A few iron nodules present and crystals of selenite. 

 Separated from red shales above by sharp line of unconformity. 

 Along the line of separation there is a layer of gumbo, one foot 

 thick 30 



No. 2 includes the red shales found in so many places above 

 the gypsum. These red sandy shales are so characteristic, and 

 associated so conformably with the gypsum, that in this section, 

 as elsewhere, they may safely be regarded as of the same age as 

 the gypsum, 



NATURE OF THE GYPSUM BEDS. 



All of the gypsum in Webster county, except the scattered 

 crystals of selenite in the Coal-Measure shales, is stratified in 

 heavy layers which are rarely less than six inches thick, com- 

 monly twelve inches or more, attaining a maximum thickness of 

 two feet. The layers are separated by traces of cla}'. In thick- 



