278 GEOLOC J Y OF I L L 1 N ( )TS. 



quite different from that presented by it at the outcrops along the Illi- 

 nois river and the upper Mississippi, and two of the most common Bracli- 

 iopods here, the Product us nuiynm and Chonetea plano-conre.ra, we have 

 not met witli in any exposures of this formation north of St. Louis. The 

 criuoids also are, for the most part, specifically distinct from those most 

 common at more northern localities, and seem to be more nearly allied 

 in form to those occurring at Crawfordsville, Indiana. The shales form- 

 ing iSTos. 2 and 3 of the above section are most probably the stratigraphi- 

 cal equivalents of the geodiferous shales of the more northern localities, 

 though we found no geodes in this county, except those of very small size, 

 and these seldom well crystalized on their interior surfaces. If we are 

 right in this conclusion, then the overlaying regularly-bedded limestone 

 is a local deposit, which seems the more probable from its containing some 

 fossils that are not known to occur at any locality north of this county, 

 such as ProHuctm magnus, ard Chonetes plano-convexa. The fossils of 

 these upper beds have a striking resemblance to those from Crawfords- 

 ville, Indiana. 



Burlington Limestone. This limestone is confined in its outcrop to the 

 vicinity of Salt Lick Point, where it forms the upper escarpment of the 

 bluff, and is also well exposed on some of the small streams that inter- 

 sect the river bluffs in this vicinity. Its thickness here probably does 

 not exceed seventy -five feet, and it consists of alternations of light-gray 

 crinoidal limestone and chert, the latter at some points predominating. 

 A section of the beds forming the bluff at Salt Lick Point shows the 

 following order of succession : 



Feet. 



1. Covered slope, apparently composed of loess 125 



2. Burlington limestone 70 



3. Ashen-gray shales and chocolate-colored limestones 80 to 90 



4. Massive gray Trenton limestone 100 to 120 



This is believed to be the highest bluff between St. Louis and Ches- 

 ter on the east side of the river, and the view from its summit is very 

 fine. St. Louis is distinctly visible to the northward, and the valley of 

 the Mississippi, for a distance of at least fifty miles by the meauderings 

 of the river, with a large portion of the American Bottom, dotted with 

 lakes and cultivated farms, may be seen at one view, forming one of 

 the finest landscapes to be seen in the State. This is the most westerly 

 extension of the bluffs in the county, and from this point they trend 

 south-eastwardly to the Randolph county line. A half-mile below this 

 the Burlington limestone forms the lower escarpment of the bluff, and 

 with a rapid dip to the southward soon disappears below the surface. 

 No exposure of this limestone was met with in the county, except those 

 occurring in this vicinity. 



