ECOLOGICAL CROSS SECTION OF THE MISSISSIPPI. 



139 



carbonate of lime, in other 



mixed 



are 



horizontal, having a slight inchnation to the northeast. The 



detailed descript 



development 



des 



the Mississippi bctwe( 

 and the mouth of the Meramec. It contains many character- 

 istic fossils. The total thickness of the St. Louis limestone 

 is estimated at 250 feet, of which^ 



along the bluff, from 

 to 120 feet are exposed. The entire section is as follows: 



r St, Louis 250 ft. 



Keokuk 225 ft. 



Lower Carboniferous. . . <| Burlington 200 ft. 



Chouteau. ..... 65 ft. 



Lower Silurian 800 ft. 



THE MISSISSIPPI RIVER. 



The Mississippi River^ which in our section closely follows 

 the bluffs on the western side, is of varying depth. Its chan- 

 nel, which for the greater part is situated on the Missouri 

 side, varies in depth from 10 to 58 feet^f and is cut in the 



ahuvial deposit. 



The depth of the alluvial deposit is not known with exacti- 

 tude. Todd says: "At St, Louis there are varying depths 

 from low water to bedrock: at the east end of the Eads bridge 

 it is 95 feet; at the east pier of Merchants' bridge it is 45 feet, 

 in a well at the Tudor Iron Works 79 feet." The bedrock 

 is the St. Louis limestone. 



THE ILLINOIS SECTION. 



In the Illinois section, the Quaternary, Carboniferous and 

 Silurian systems are recognized.^ The Quaternary system, 

 quantitatively, in depth as well as in area, is better repre- 



sented than in the Missouri section. 



Amer. Joura. 



* Engelmann, G. Remarks on the St. Louis Limestone. 

 Sci. and Arts. 2 ser, 3 : 119. 1847. 



t Sm-vey of the Mississippi River, made under the Direction of the 

 Mississippi River Commission. Chart 114. 



Worthen 



Geological Survey of Illinois. 1 : 21. 1866. 



1 



