152 THE DEVONIAN AND CARBONIFEROUS. [bull. 80. 



Iu the report of the geological survey of 'Iowa, a systematic study of 

 the fossils of the Mississippiau series was applied iu the differentiation 

 of the several formations. 1 



The geological formations of the upper Paleozoic were classified in 

 the following manner by James Hall : 



Above the Le Claire limestone comes a hydraulic, drab-colored lime- 

 stone and shales with cavities, called the " Onondaga salt group"; next 

 above this a limestone, gray and ash-colored, subcrystalline, also con- 

 taining cavities, and with shaly partings, called the " Upper Helder- 

 berg;" following this is an argillaceous limestone or calcareous shale 

 called the " Hamilton," which in some places is an alternation of cal- 

 careous shales and limestones, but is said to be more calcareous at the 

 bottom. A stratum 10 to 15 feet thick at Rockingham and New Buf- 

 falo is called the " Encrinal limestone." Next above are shales and 

 soft sandstones, as at Pine Greek, called the " Chemung." The order 

 observed at this last mentioned place for the Chemung is " shaly lime- 

 stone, green shale, sandy beds, yellow sandstone." At Davenport, 

 Burlington, etc., the Chemung is described as "gray and yellow sand- 

 stone with shaly partings." Sometimes it is underlain by green shales, 

 which are called the " Portage group." 2 



The typical section of this part of the series is at Burlington, Iowa. 3 

 It is as follows : 



(1) Soft green shale. (2) Fine grained siliceous and argillaceous sandstone. (3) 

 Limestoue and shale, siliceous. (4) Argillaceous sandstone with Chemung fossils. 

 (5) Oolitic bed. (1-5— " Chemung group".) (6) Calcareous and argillaceous shale, 

 beds of passage. (7) Cherty beds. (8) Burlington limestone, brownish or grayish- 

 brown encrinal limestone, the higher beds more or less white and subcrystalline, 

 and in places 72 feet thick. 



This Burlington limestone was regarded by Hall as equivalent to the 

 "Encrinital limestone" of Owen of Missouri. It thickens southward. 



Following the " Chemung " occurs a light gray or brownish white crin- 

 oidal, subcrystalline limestone called the u Burlington limestone." Upon 

 this comes the " Keokuk limestone," a shaly grayish or bluish crin- 

 oidal limestone, which the author regarded as an equivalent of the "Ar- 

 chimedes limestone " of Owen and the iC Siliceous group " of Tennessee. 

 The Keokuk is followed by a geode bed and this by the " Warsaw lime- 

 stone or second Archimedes limestone," which is " a magnesian lime- 

 stone, shale and shaly limestone, thin-bedded and arenaceous," and after 

 this a " coarse yellow calcareous sandstone and some pebbles of quartz." 

 Next comes the " St. Louis limestone" of Swallow or "Concretionary 

 limestone" of Owen. This is a brecciated, ash colored limestone, and 

 sometimes subcrystalline and granular in texture, becoming more com- 



1 Report on the Geological Survey of the State of Iowa, embracing the results of investigations made 

 during portions of the years 1855, 1856, and 1857, hy James Hall and J. D. Whiting, vol. 1, Albany, 1858. 

 8vo., xv, 724, 4, and 30 pp., 29 plates, plate of section, and 2 maps. 



2 Ibid., p. 89. 



* Ibid., pp. 89-90. 



