12 GEOLOGY OF ILLINOIS. 



to this group, and consider it as probably replacing the green shale, which 

 forms the base of the group at nearly all the other localities, where we found 

 the lower beds exposed in this county. This is the only point south of the 

 Crip au Ores axis, where we met with any exposure of the Kinderhook beds, 

 in the county. 



Burlington Limestone. This division of the Lower Carboniferous series, out- 

 crops over a wide area in this county, and forms the bed-rock over nearly all 

 the high lands north of the Cap au Ores axis. It forms the upper escarpment 

 of the river bluffs, from the north line of the county, to Hamburg on the west, 

 and to the vicinity of Monterey on the east, and also outcrops on most of the 

 small streams in the northern part of the county. Its entire thickness ranges 

 from one hundred and fifty to two hundred feet, but it is usually only partially 

 exposed, a considerable portion of it being hidden, either in the covered slope 

 at the top of the bluff, or in the sloping talus below. 



At Reed's Landing, about two miles and a-half below the north line of the 

 county, the bluffs of the Illinois are about two hundred and forty feet in bight, 

 nearly one-half of which is Burlington limestone, forming a natural cliff a 

 hundred feet or more in bight. Below the limestone cliff, there is a sloping 

 talus, to the level of the bottoms bordering the river, covering the shales 

 of the Kinderhook group, which probably extend from the base of the lime- 

 stone down to the river level. This limestone is generally coarse grained or 

 granular in texture, of a gray or brownish gray color, and tolerably regular 

 bedded, the strata varying from four inches to two feet in thickness. It con- 

 tains a good deal of cherty or flinty material, which occurs either in nodules, or 

 in regular seams intercalated in the limestone strata. The term "Crinoidal 

 limestone" which has sometimes been applied to this rock, is very applicable to 

 the upper portion of it in this county, as it is almost entirely composed of the 

 remains crinoidea, and other marine animals, cemented by calcareous matter. 

 The chert with which the limestone abounds, is also filled with the silicified 

 remains of these marine animals, and it affords exquisite casts, in flint, of the 

 internal structure and markings of many of the organic bodies of which this 

 limestone is so largely composed. Casts of several species of Actvnocrimu, one 

 species of Platycrinus and Granatocrinus Norwoodi, were obtained from the chert 

 nodules at this locality, and from the limestone we obtained Spirifer Grimesi, 

 Strophomena analoga, and Euomplialus latus. The lower portion of this lime- 

 stone here, as elsewhere in this county, consists of alternations of gray and 

 light yellow, or brown, earthy or magnesian limestone, only slightly crinoidal 

 in its character, but finer grained and more compact than the upper beds. It 

 contains very few well preserved crinoids, though detached columns and crushed 

 bodies are frequently met with. In some respects, these brown beds would 

 seem to correspond to the lower division of this formation at Burlington, Iowa, 



