SUBDIVISIONS IN GEOLOGICAL HISTORY. 407 



Stages. For intermediate divisions sub is prefixed to the name of the 

 division next above. Still lower subdivisions are termed zones, and receive 

 special designations from a characteristic fossil. Subdivisions of zones, 

 corresponding to the vertical distribution of species, have been recently 

 called hemercB, from the Greek for day. In place of any of the above 

 terms, the word time may be used in its usual sense whenever it is thought 

 convenient. It is substituted beyond for the word oeon. 



I. Arch^an" Time. — The beginning of Archaean time was without life ; 

 but before it closed conditions had been reached that admitted of the exist- 

 ence of protophytic and protozoic life. 



II. Paleozoic Time. — Characterized by the more ancient kinds of life, 

 closing with the period of the great Coal formations of Europe and America, 

 so named from TraAatos, ancient, and ^wr;, life. 



III. Mesozoic Time. — The life of mediaeval types or kinds; closes with 

 the period of the Chalk or Cretaceous formation, so named from /aco-os, 

 middle, and t.oi-q. 



IV. Cenozoic Time. — The life of more modern types, continuing to the 

 present time, so named from Katvos, recent, and ^wiy. 



The term Paleozoic was proposed by Sedgwick in 1838, and preferred and adopted by 

 MurcMson the same year in place of his own name Protozoic, it "involving no theory." 

 For the terms Mesozoic and Cenozoic, and the upper limit of the Paleozoic, the science is 

 indebted to Professor John Phillips, of Oxford, England. Cenozoic is sometimes written 

 Cainozoic or Kainozoic. But in English, derivatives from the Greek diphthong at become 

 «e or e, as in Ethiopia, Eolian, Egypt, Etna, ether, hematite ; and k becomes c, as in center, 

 circle, calyx, camel, and multitudes of other words. Lyell's names for divisions of the 

 Tertiary, namely, Eocene, Miocene, Pliocene — are examples of both cases, the ce in 

 each being /cat in Greek. 



The following table contains some of the subdivisions of inferior grade : 



I. ARCH.^AN TIME. 



There are the two divisions, the Azoic and the Aech^ozoic, but they are 

 not distinguishable in the rocks. The rocks have been divided into — 



1. Laurentian. 



2. huronian. 



II. PALEOZOIC TIME. 



1. Eopaleozoic Section. 



1. Cambrian, or Cambric, Era. 



1. Lower Cambrian, or Georgian Period. 



2. Middle Cambrian, or Acadian Period. 



3. Upper Cambrian, or Potsdam Period. 



2. Lower Silurian, or Lower Siluric, Era. 



1. Canadian Period. 



2. Trenton Period. 



