146 MISSOURI BOTANICAL GARDEN. 



thin coal scam. There is an outlier of this limestone on 

 the south side of the anticlinal axis that intersects 

 the river bluffs just above the Monroe county line. North 

 of this axis we did not find this limestone exposed anywhere 

 in the river bluffs in this county. The lower sandstone of 

 the Chester group underlies the limestone just described 

 and its outcrop is consequently over a belt of country to the 

 south and west of that occupied by the limestone. The 

 St. Louis limestone makes its first appearance in the river 

 bluffs about 3 miles below Centerville station, where it 

 comes UD from beneath the sandstones just describcid, and 



Mon 



main portion of the bluff from 

 itv line. At the old lime-kili 



rlit forms a mural cliff from 



high and continues gi'adually increasing in elevation to 



Fallin 



the level of the Mississippi Bottoms. It presents here its usual 

 characters of a regularly bedded fine-grained hmcstone, of a 

 light gray color and compact structure. The beds vary in 

 thickness from 3 inches to 2 feet or more. The upper por- 



and 



iapted 



as it is at St. Louis and Alton. As we approach the Monroe 

 county line the beds continue to rise and the brown mag- 

 ncsian and semi-oolitic Umestones that constitute the lower 

 division of this group are elevated above the surface and com- 

 pose the main portion of the bluff at the anticlinal axis, about 

 1 mile above the southern line of the county. Immediately 

 below the axis the upper beds of the group again form the 

 entire bluff, and with a reversed dip, at an angle of about 

 30 degrees, they plunge below the level of the Mississippi 

 Bottom. The uppermost beds of this group are well exposed 

 in the vicinity of Lark's quarries, about 4 miles from the 

 Centerville station. At this locality the upper layers of the 

 limestone are quite massive and afford solid blocks of lime- 

 stone from two and one-lialf to three feet thick. . , . 

 At the old lime-kilns, above Falling Spring, we obtained 

 some characteristic fossils. . . . This lim(^stone out- 

 crops only over a very Hmited an^a in the southwest corner 



