THE WORLD IN THE MAKING 31 



Under the eras, periods, and their subdivisions are given at 

 the left the names of the better-known formations belonging to 

 each, mostly those of the eastern states, while at the right are 

 those of Illinois and adjacent regions. Unless the names are 

 identical, those on the same line in the two series are not to be 

 taken as necessarily equivalent. 



Cenozoic Era 



Quaternary 



Recent period 



Pleistocene period 

 Tertiary 



Pliocene period 



Miocene period 



Oligocene period 



Eocene period 



Mesozoic Era 



Cretaceous period 

 Comanchean period 

 Jurassic period 

 Triassic period 



Paleozoic Era 



Permian period 

 Upper Permian 

 Rustler 



Castile gypsum 

 Lower Permian 

 (Brazos or Oklahomian) 

 Delaware Mountain 

 Dunkard shales, sand- 

 stones, and limestones 

 Pennsylvanian period 



Monongahela shales, sand- 

 stones, and limestones 

 Conemaugh shales, sand- McLeansboro series, including clay, 

 stones, and limestones limestone, slate, sandstone, and 



the LaSalle first-vein coal, also 

 known as Streator No. 7 

 Allegheny shales, sand- Carbondale series, clay, limestone, 

 stones, and limestones slate, sandstone, and LaSalle 



