Excerpt from The Age and Origin of the Gypsum, Deposits of Central Iowa: A Dissertation Submitted to the Faculty of the Ogden Graduate School of Science, in Candidacy for the Degree of Doctor of Philosophy, Department of Geology
The known gypsum of Iowa is confined to Webster county, which lies somewhat north and west of the center of the state. Here it occupies a tract about six miles wide and fifteen miles long, on the edge of which the city of Fort Dodge is located. The original gypsum area has been greatly reduced by the erosive and solvent action of the Des Moines River, which crosses it nearly at right angles, cutting completely through it and deep into the Coal Measures beneath. Some of the earliest geological work undertaken in the state was carried on in this region. The Des Moines River exposes along its banks the indurated rock and gives at times sections of rock and drift 200 feet in thickness, which greatly facilitate geological study. The unique deposit of gypsum has been attractive to the student on account of the theoretical problems that it presents, and to others it is interesting on account of its practical value.
In the year 1849 Owen made a hurried trip up to the Des Moines River, noticed the gypsum, and made certain deductions in regard to its origin. After describing its remarkable thickness and purity, he adds:
This plaster stone of the Des Moines does not appear to have been deposited in nests or conical heaps, as in the shales of the Onondago Salt Group of New York, but rather in continual horizontal beds, conformable to the underlying shale.
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