MONROE rnrxTY. 277 



division of the St. Louis group; a ml from this point to the south line of 

 the county, they are well exposed at many points in the river bluffs. 



Keokuk group. The outcrop of the upper portion of this group, where 

 it forms the nucleus of the anticlinal axis passing a half mile east of Co- 

 lumbia, has already been mentioned, but good exposures are rare, and 

 only a few feet in thickness of these beds are to be seen at the various 

 localities examined along the trend of this axis. At Mr. Ditch's place, a 

 half mile north of Waterloo, on the Columbia road, a well was sunk to 

 the depth of about a hundred feet, the first 20 feet being drift clay, and 

 the remainder through the shales and limestones of the Keokuk group. 

 This is evidently near the center of the axis, as a mile and a half north- 

 east of this point the hard gray limestones of the upper division of the 

 St. Louis group outcrop at the surface, dipping eastwardly at an angle 

 of about 5 (leg. Two miles and a quarter north-west of Waterloo, on the 

 road leading in the direction of Gall's coal bank, a yellow calcareous 

 shale, with intercalated plates of chert and limestone, are found out- 

 cropping on a small creek running to the westward into Fountain creek. 

 Tnis shale contained small quartz geodes, and the plates of limestone 

 afforded specimens of A rehiniedes Otcena)ia,8pirifer liHeatus, 8. cmpidatm, 

 and some other organic forms of the Keokuk group. 



One of the best exposures of this group seen in the examination of this 

 county was found on Mr. Prior's place, about a mile aud a half to the 

 eastward of Salt Lick Point. The beds at this locality afforded the fol- 

 lowing section: 



1. Coarse grained gray limestone 25 to 30 feet. 



2. Yellow calcareous shales 12 " 



3. Slope, with partial outcrops of blue shale 35 " 



1. Cherty iU'ay limestone 60 " 



5. Bedded chert 6 " 



143 



The upper limestone in the above section is a good building stone, 

 and contained the characteristic fossils of this horizon, among which we 

 observed Spirl/cr Kcokuk, Productits magmis, and Terebratula liatstata. 

 The bedded chert at the base of the section may possibly belong more 

 properly to the Burlington, than to the Keokuk series. 



In the river bluffs two miles west of Glasgow, the lower portion of 

 the bluff consists of the shales and thin-bedded limestones of this group^ 

 of which a hundred feet or more in thickness is here exposed. These 

 beds are full of fossils, among which Spirifer Keokuk, S. cuspiflatiis, Pro- 

 ductus mfiyHii,*, and ('honctex plcnw-coni'e.ra. are quite abundant, associa- 

 ted with several species of rare crinoids, among which are the Onycho- 

 t-rlnm Monroensix and Zeacrinux plann-bruch'uitHx, lignred and described in 

 the second volume of these reports, with several other as yet undeter- 

 mined forms. The lithological character of the rock in this county is 



