COUNTY, 



Keokuk Limestone. This is the lowest rock exposed in the county, 

 and is only found along the bluffs of Crooked creek, in townships 4 and 

 5 north, range 4 west. The upper part of this formation is usually a 

 bluish calcareo-argillaceous shale, containing silicious geodes either 

 filled with a mass of crystaline quartz, or hollow and lined within with 

 quartz crystals, maiunhllary chalcedony, calcite and dolomite. Below 

 this geode bed there is usually from thirty to forty feet of cherty gray 

 limestone, the layers varying in thickness from a few inches to two feet 

 or more, and separated by partings of shale. The limestone beds con- 

 sist mainly of the remains of organic beings, the corals, crinoids and 

 mollusca that swarmed in countless numbers in the primeval ocean, and 

 the old quarries in this limestone afford a rich field for the student who 

 desires to become fully acquainted with the varied and peculiar organic 

 forms of this period. South of Colmar the grade of the C., B. and Q. 

 railroad cuts into the upper part of this limestone to the depth of seve- 

 ral feet, and from the material thrown out from this cut we obtained many 

 specimens of the characteristic fossils of this limestone in an excellent 

 state of preservation. The upper layers of the limestone had been 

 freely exposed to the erosive action of the writer during the drift period, 

 and many of the silicious fossils were found completely weathered out 

 from the shaly limestones, and in a most perfect state of preservation. 

 Among the fossils found at this locality were many specimens of Zaph- 

 rentis daUi, Spirifer Keokn.l\ S.Uneatns, S.sub-orbicularis. Agaricocrinus 

 Americanus. Actinocrinus bi-titrbinatiis^Cyathocrinus stellatus, Archimides 

 Oicenana, Hemiproniies crenistria, Phillipsia Portlockii, several species 

 of fish teeth, etc. The lower portion of this limestone is usually below 

 the level of the creek bottoms, but the upper portion is well exposed on 

 the main creek in T. 4 X.. R. 4 VT., and on the east fork in T. 5 X., R. 4 YV. 

 In the region south of Colmar the geodiferous shales and the St. Louis 

 limestones have all been removed by denudation before the depost of 

 the drift, and the boulder clays now rest directly upon the upper part of 

 the Keokuk limestone. A complete section of all the limestones below 

 the Coal Measures in this county would show the following order of suc- 

 cession and thicki; 



Light-gray brecciated limestone 5 to 20 feet. 



Calcareous sandstone 12 " 



Magnesian limestone and shale 10 " 12 " 



Geodit'erons shales of the Keoknk beds 520 "30 " 



Light-gray cherty limestone 30 " 40 " 



E c o n o m i c a I G e ol o g ij . 



Coal. As may be seen from a perusal of the foregoing pages, a large 

 portion of this county is underlaid with coal, and although the seams 

 that are found here are much thinner than some of those that outcrop 



