TIME DIVISIONS 



323 



CKM.KAI. IABU-: OF GEOLOGIC TIME DIVISIONS 1 



Cenozoic 



Ouaternary 



Tertiary 



Mi'sozoic 



Paleozoic 



1'roterozoic 



Archeozoic 



Present 

 Pleistocene 

 T Pliocene 

 j Miocene 

 "] Oligocene 

 [ Eocene 



Transition 



f Cretaceous (Upper Cretaceous) 

 | Comanchean. or Shastan (Lower Cretaceous) 

 T Jurassic 

 [ Tfiassic 

 Permian 

 Pennsylvanian (Coal Measures) 



Wide-spread unconformity 

 Mississippian (Subcarboniferous) 

 Devonian 

 Silurian 



1 1 "idc-xpredd unconformity 

 Ordovician 

 Cambrian 



Great unconformity 

 Kcweenawan 



/ ' n<:nnjnrmity 

 Upper Huronian (Animikean) 



Unconformity 

 Middle Huronian 



Unconformity 

 Lower Huronian 

 Great unconformity 



Archean Complex 



Great Granitoid Series 

 (Intrusive in the main; 

 Laurentian) 



Great Schist Series 



(Mona, Kitchi, Keewatin, 

 Quinnissee; Lower Huronian 

 of some authors) 



THEORETICAL CONSIDERATIONS 



Bearing on theories of the earth's origin. With the essential r 

 facts concerning the constitution and structure of the Archean in 

 mind, it is in order to inquire to what hypothesis of the earth's 



1 There are many unconformities not suggested in the table, where only those 

 which appear to be extensive are noted. Those between the systems of the Pro- 

 terozoic are known to be general for the Lake Superior region only. 



