ARCHEAN AND PALEOZOIC GEOGRAPHY 447 
in a world peopled by man. This change toward present condi- 
tions involved the purification of both air and water of noxious 
gases and other substances unfavorable to the existence of life. 
With the coming of organisms in the clearer waters of the 
globe, there also appeared more quiet conditions of air and water 
action, and less activity within the earth itself, which was now 
less highly heated near the surface. It is only after the intro- 
duction of these new conditions of air and water action, and after 
life had taken possession of the waters of the ocean, and part of 
the land, that the geological record becomes really readable. 
This which has preceded is speculation ; that which 
follows is mainly fact obtained from the record of the 
rocks. It is possible that the ancient history of the 
earth has been quite different from that just stated ; 
but it 1s probable that the later history, as stated in the 
following pages, will not be changed in its essential 
principles. 
Archean Geography. — At the close of the Archean, 
the United States was partly above the sea and partly 
beneath it (Fig. 261). There were three distinct land 
areas. One, in the east, stretched from north of New 
England as far south as Georgia, and perhaps beyond. 
The second included the greater part of Canada, ex- 
tending from the Arctic down to the United States 
boundary, which it crossed in at least two places, one 
in the Adirondack region, the other near Lake Superior. 
The third area was in the Far West, along the ranges 
of mountains which later became the Cordilleras. 
