724 FRANK A. WILDER 



upper Des Moines can hardly be accounted for on the principle of double 

 chemical decomposition between sulphate of iron and carbonate of lime, for- 

 merly existing where the plaster now is, since there does not appear to be an 

 equivalent bed of iron in the vicinity, nor yet beds of limestone, except thin 

 bands of black bituminous, calcareous rocks, by no means extensive, that are 

 in immediate connection with the plaster-beds. It seems rather to have been 

 an original deposit at the bottom of the ocean ; the sulphate of lime having 

 probably been derived, during the formation of the rocks, from submarine 

 sources. 



In 1856 Worthen' visited the region and came to the conclu- 

 sion that the gypsum does not lie conformably on the Coal 

 Measures. Hall^ in 1858 and McGees in 1884 considered the 

 stratigraphic relationship and age of the gypsum. Webster 

 county was included in the geological studies of C. A. White and 

 references to coal and gypsum are made in his annual reports of 

 1868 and 1870.^^ In these reports White pointed out the great 

 value of the Webster count}^ gypsum, and urged that it be devel- 

 oped so that the state might furnish the stucco and land plaster 

 used within its borders. 



Keyes5 reported quite fully on the gypsum area in 1893, 

 describing the position and the extent of the deposit and its 

 stratigraphic relationships, and with reference to its age con- 

 cluding that it should be referred to the Cretaceous. 



GENERAL RELATIONS OF STRATA. 



Excepting limited Carboniferous outliers, Webster county 

 contains the most northern of the Iowa Coal Measures. These 

 lie just beneath the drift throughout the southern part of the 

 county, and extend north to a point three miles above Fort 

 Dodge. The Saint Louis limestone underlies the drift in the 

 northern part of the county, and appears along the Des Moines 

 well to the south, where the stream has" cut through the Coal 

 Measures. Upon the Coal Measures in the central part of the 

 county lie the gypsum beds unconformably. The term "gypsum 



' Geology of Iowa, Vol. I (1858), p. 177. "Ibid., p. 142. 



3 Tenth U. S. Census, Vol. X, "Building Stones," p. 258 (Washington, 1884). 



^ First Annual Report State Geologist {l%b^), pp. 25-27; Second Annual Report 

 (1868), pp. 135-40. Geology of loxva. Vol. II, pp. 293, 254-56. 



^ Iowa Geological Survey, Annual Report, Vol. Ill (1893), pp. 259-304. 



