198 New York State Museum 



tent of Archeozoic rocks is found in eastern Canada in 

 an area of about 2,000,000 square miles that forms an 

 irregular mass around Hudson bay and extends south 

 into Wisconsin and Minnesota. This is known as the 

 Canadian or Laurentian Shield in which some geologists 

 have included Greenland and the Adirondacks of New 

 York State. Crystalline rocks partly of Archeozoic age 

 appear in New England and in a belt stretching from 

 Maryland south to Alabama (the Piedmont Plateau 

 area). Archeozoic rocks are also found in the western 

 part of the continent forming the cores of the mountains 

 and in isolated patches elsewhere. The Canadian Shield 

 is chiefly formed of the widely distributed Laurentian 

 gneisses and granites which represent numerous batho- 

 liths that welled up into the earlier sediments (Keewatin 

 and Grenville series). 



In the lowest Archeozoic series are the oldest sedi- 

 mentaries known (Coutchiching formation), typically 

 exposed in the Rainy Lake district of Canada north of 

 Minnesota. They consist of graphitic mica-schists, de- 

 rived by metamorphism from carbonaceous shales, and 

 dolomites, both probably of marine origin and showing 

 a thickness of 4600 feet. The Keewatin series, overlying 

 the above, has a wide distribution and is best known in 

 the Lake of the Woods area in the extreme western part 

 of Ontario. This series has a thickness ranging from 

 6500 to 23,700 feet and consists of a succession of dark 

 lava flows, ash beds and black carbonaceous and sandy 

 mudstones. The lava flows are usually basalts meta- 

 morphosed to greenstones and green schists, and the mud- 

 stones have also been altered to schists. The upper 1500 

 feet of this series consists of interbedded banded jasper 

 and iron ore and also contains limestones. The iron ore 



