GEOLOGIC DIVISIONS MAPPED. 15 



MIDDLE AND LOWER HUBONIAN. 



Color, brown with red dashes. 



Symbol, 22b. 



Distribution: Lake Superior region; Ontario, Minnesota, South Dakota, Wisconsin, and Michigan. 



Content: Sedimentary and intrusive rocks in the Lake Superior region only; Sioux quartzite of 



South Dakota and Baraboo quartzite of Wisconsin. Areas mapped include intrusive 



igneous rocks. 



" LAURENTIAN " (CANADIAN USAGE). 



Color, pink and red hachures. 



Symbol, 23. 



Distribution: Throughout Canada and the Arctic. 



Content: Gneisses and associated plutonic rocks throughout Canada, the Laurentian of Cana- 

 dian geologists; included in Archean of Dana. (Areas of undifferentiated pre-Cambrian 

 in Michigan, Wisconsin, Minnesota, and North Dakota have also been mapped under this 

 color.) 



LATJRENTIAN (OF THE LAKE SUPEEIOE EEGIOn) . 



Color, pink with red hachures. 

 Symbol, 23d. 



Distribution: Wisconsin, Michigan, and Minnesota. 



Content: Acidic plutonic rocks intrusive in Keewatin, separately indicated only within the 

 United States. 



, i^CEEWATIN. 



Color, dark red with white hachures. 



Symbol, 23a. 



Distribution: Lake Superior region; Ontario, Michigan, Minnesota, and Wisconsin. 



Content: Oldest pre-Cambrian of the Lake Superior region. Largely basic lavas. 



UNDIFFERENTIATED PRE-CAMBRIAN. 



Color, pink with red dashes. 



Symbol, 23b. 



Distribution: Appalachian province, Vermont to Alabama; Missouri, Texas, Arizona, New 

 Mexico, California, and the Rocky Mountains of the United States; in Michigan, Wiscon- 

 sin, Minnesota, and North Dakota is mapped under " 'Laurentian' (Canadian usage)." 



Content: Gneisses known to be of pre-Cambrian age, but not otherwise correlated; included in 

 Archean of Dana. Includes plutonic igneous rocks where not separately mapped, and 

 some sediments of Paleozoic age. 



GNEISSES, SCHISTS, AND METAMORPHOSED SEDIMENTS (SUPPOSED PRE-CAMBRIAN; POSSIBLY IN 



PART PALEOZOIC AND MESOZOIC) . 



Color, pink with blue dashes. 

 Symbol, 23c. 



Distribution: In the Cordillera from South America to Alaska. 



Content: Highly metamorphosed schists and associated plutonic rocks, apparently of great 

 antiquity but not known to be pre-Cambrian; possibly in part Paleozoic or JMesozoic. 



PRE-CAMBRIAN INTRUSIVE ROCKS. 



Color, dark violet. 



Symbol, 24. 



Distribution: Plutonic igneous rocks in eastern Canada, eastern United States, and Oklahoma. 

 Includes some effusive rocks of same age. Elsewhere mapped with associated pre- 

 Cambrian rocks. 



