1G6 



THE DEVONIAN AND CARBONIFEROUS. 



[bull. 80. 



strata represented within the State, 

 follows : 



Above the Silurian they are as 



1. Black slate formation, at the base, 



2. Siliceous formation, or the series of cherty limestones, 



3. The Argillo-limestone formation, called the Mountain limestone, 



4. The Lower Coal Measures, separated by 



5. The conglomerate from the 



6. Upper Coal Measures. 



Fossils were reported and were used in correlating the several for- 

 mations, but the subdivisions were much less finely drawn than in Illi- 

 nois, Missouri, or Iowa, where fossils were more abundant in the Mis- 

 sissippian series. 



The classification of the Lower Carboniferous formations into two 

 groups, the "Siliceous" and the "Mountain limestone," is worthy of 

 attention, but until the faunas are thoroughly studied this can not be 

 considered as final. A comparison of the various faunas reported from 

 the " Subcarboniferous," or "Lower Carboniferous" formations of the 

 interior had already demonstrated considerable difference in the asso- 

 ciation of species in different parts of the area, but of the marine faunas 

 the line which appears generally more sharply drawn is that between 

 (a) the St. Louis (and, where present, the Warsaw,) and (b) the fauna 

 next below, as the Keokuk and Burlington. 



In the reports of the second survey of Iowa, 1 some modification of the 

 classification proposed by James Hall in 1858 is seen. Mr. White re- 

 ported in volume 1 the following classification : 



Feet. 



f Upper 200 



<( Middle 200 



l Lower 200 



TSt. Louis limestone 75 



< 



Carboniferous < 



Coal Measures. 



Subcarboniferous 



Keokuk limestone 



90 



, Burlington limestone 190 



I Kinderhook beds 175 



Devonian Hamilton Hamilton shales and limestone 200 



Silurian Niagara limestone 



Mr. White referred all the Devonian strata of Iowa to a single for- 

 mation, the Hamilton group of New York, and did not recognize any 

 representative of either Upper Helderberg or Chemung. The Carbon- 

 iferous system is present in only the two members, which he called 

 "Subcarboniferous" and "Coal Measures." He used "Subcarbon- 

 iferous group" as synonymous with the old terms " Carboniferous lime- 

 stone," " Subcarboniferous limestone," and " Mountain limestone." In 

 the subdivision of this group and its nomenclature he evidently follows 

 the first and second Illinois reports. 



Mr. F. B. Meek 2 wrote a report on the Spergen Hill fossils in 1873. 



1 Report on the Geological Survey of the State of Iowa to the Thirteenth General Assembly, for 

 1870, containing results of examinations, etc., made 1866, 1867, 1868, and 1869. By Charles A. White, 

 M. D. Vol. 1, 1870. 



3 Meek, F. B. : Spergen Hill fossils identified among specimens from Idaho. Am. Jour. Sci., 3d ser., 

 vol. 5, 1873, pp. 383, 384. 



