THE ARCHEOZOIC ERA. 161 



The following classification of the pre-Cambrian has recently been proposed 

 by a Committee of the United States and Canadian Geological Surveys 

 appointed to consider the question : 



Cambrian — Upper sandstones, etc., of Lake Superior. 



Unconformity. 

 Pre-Cambrian. 



Keweenawan (Nipigon). 

 Unconformity. 



' Upper (Animikie). 

 Unconformity. 

 Huronian. • Middle. 



Unconformity. 

 L Lower. 

 Unconformity. 

 Keewatin. 

 Eruptive contact. 

 Laurentian. 

 The Lower and Middle Huronian of this table, 1 taken together, correspond 

 to the Huronian of the table above. This classification was published after 

 this chapter was in the hands of the printer, and has therefore not received, in 

 the pages which follow, the consideration to which its history entitles it. It 

 will be noted that its principal departure from the preceding classification lies in 

 the threefold, instead of twofold, division of the rocks between the Archean 

 below, and the Keweenawan above. 



1 Jour, of Geol., Vol. XIII, p. 104. 



