THE OVERLAND EOUTE COUNCIL BLUFFS TO OGDEN. 



15 



Nearly yertical walls of it have stood practically unchanged for 30 

 years/ and other equally precipitous walls have the appearance of 



being much older. 



limest 



and sandstone of Carboniferous age/ which have been penetrated by 



^ The only Paleozoic rocks which come 

 to the surface in eastern Nebraska belong 

 to the Carboniferous system, deposited at 

 a time when most of the coal beds in the 

 eastern part of the United States were in 

 process of formation from vegetal deposits. 

 (For types of Carboniferous vegetation see 



PI. IV, C, p. 20.) They are economically 

 the most important rocks in the State. 

 Most of the building stone, clay, and 

 lime produced in Nebraska come from 

 them. Their relations to other rock for- 

 mations exposed in eastern Nebraska are 

 shown in the followingr table: 



Geologic column showing relations of rocks exposed in eastern NehrasTca. 



Age. 



Character. 



Quaternary 



Kansan drift 



Glacial till. 



Aftonian gravels. 



Sand and gravel; locally conglomerate. 



Pre-Kansan or Nebras- 

 kan drift. 



Tertiary 



Cretaceous. 



Niobrara limestone. 



Glacial till 



Sand and clay 



Chalkv limestone and shale 



Benton shale. 



Carboniferous 



Blue shale with limestone concretions 

 (Carlile shale.) 



Hard slaty limestone and blue chalky 

 clay. (Greenhorn limestone.) 



Dark sandy shale. (Graneros shale.) 



Dakota sandstone. 



Soft massive yellow sandstone. 



Limestone, sandstone, and shale of Per- 

 mian and Pennsylvanian age. 



In eastern Nebraska the Carboniferous 

 beds that a{)pear at the surface comprise 

 200 feet of Permian and 1,200 feet of Penn- 

 sylvanian rocks. The lowest series of the 

 Carboniferous, the Mississippian, does not 

 outcrop here. Tlie Pennsylvanian rocks 



consist of 



alternating 



limestones and 



ehales. The rock formations below the 



Pennsylvanian in eastern Nebraska are 

 of interest because they include certain 

 strata that supply water to artesian wells. 

 Several of these wells drilled in and near 

 Omaha found water at depths of 1,200 to 

 1,800 feet under pressure sufficient to flow 

 at the surface. The lowest stratum yields 

 the strongest flow. 



