ON GEOLOGIC TIME-DIVISIONS 35 I 



those of the second order a variety of different terminations exist ; 

 but it is probably not advisable now to change them. How- 

 ever, these names are so few in number that they are not liable 

 to cause confusion. The provincial titles of the third order are 

 in large part yet to be proposed. For all these an appropriate 

 original or provincial name is suggested, with the ending a?i, 

 if possible. This leaves the countless horde of formations, or 

 stages, the usual units of geological mapping, the distinguish- 

 ing characters of which are based chiefly upon lithology, a clear 

 field for unchanged, local, geographic honors. The zones are 

 named from their leading fossils. 



Our information regarding the geological subdivisions is so 

 unequally distributed that at best a very unsymmetrical classifi- 

 cation must be endured for the present. The following seems 

 to be the most acceptable scheme for North America: 



Era. Period. Epoch. 



Late or Recent. 



Early. 



Pleistocene. 

 Cenozoic. -I Neocene. 

 Eocene 



( Cretaceous. 

 Mesozoic. 4 ? 



< ? 



( Late 



f Carboniferous. ) Mid. [• For all. 



Devonian. ( Early. 



Palaeozoic. ^ Silurian. 



Ordovician. 

 [ Cambrian. 



( Keweenawan 

 Proterozoic -j Huronian? 



( Laurentian ? or new name. 



Azoic Archaean. 



For purposes of instruction the provincial scheme for rocks 

 for the special region studied may serve as a standard. 



It is desirable to adhere to European standards, or the 

 present American standards as derived from Europe, as closely 

 as possible until our present knowledge expands sufficiently to 

 enable us to gradually erect new and more rational standards. 

 The first and second orders should be as closely equivalent as 



