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HISTORICAL GEOLOGY 



Table of Geologic Divisions 



Cenozoic era and group 

 Mesozoic era and group 



Paleozoic era and group 



Proterozoic era and group 

 Archaeozoic era and group 



Quaternary period and system. 

 Tertiary period and system. 

 Cretaceous period and system. 

 Comanchean period and system. 

 Jurassic period and system. 

 Triassic period and system. 

 Permian period and system. 

 Pennsylvanian period and system. 

 Mississippian period and system. 

 Devonian period and system. 

 Silurian period and system. 

 Ordovician period and system. 

 Cambrian period and system. 

 Keweenawan 1 period and system. 

 Animikean l period and system. 

 Huronian : period and system. 

 Archaean period and system. 



Periods older than the geologic record. Back of these 

 periods and eras there stretches a vast lapse of time of w.hich 

 we know so little that the use of definite time divisions is 

 hardly justified as yet. It includes the beginning of the earth 

 and its development through a series of exceedingly slow 

 changes. 



Imperfect record of the earth's history. If we had as 

 complete a knowledge of the earth in its earlier periods as we 

 have of its present state, we should be able to construct a 

 fairly complete history of it. That would include the changes 

 which have occurred in the shapes of seas and land, in the 

 mountains, plains, and other topographic features, in the dis- 

 tribution of volcanic districts, the development of the many 

 groups of animals and plants, the fluctuations of climate, and 

 many other important things. As it is, only a part of these 

 facts have been recorded in the rocks ; only a small portion 



1 These names are applied only in the Lake Superior region of the United 

 States. The rocks which represent the oldest periods are almost devoid of 

 fossils, and it is therefore hardly possible to extend the same names to 

 other regions, as has been done in the case of later periods. 



