GEOLOGIC DIVISIONS MAPPED. 13 



SILURIAN. 



Oolor, violet. 



Symbol, 16. 



Distributioiv: General throughout northern and eastern North America east of the Great Plains; 

 represented by the Devonian color (15) in the Appalachian zone south of latitude 38°; 

 known to be present in the Cordillera and Alaska but not generally distinguished by sepa- 

 rate color, except in Mexico, Nevada, and British Columbia. 



Content: In the Appalachians in general includes Medina to Cayuga; in the southern Appa- 

 lachians is mapped with Devonian; in eastern Canada and New York Helderberg is included 

 on the map; in the Interior strata of Niagara age; in the Arctic, the SUurian color covers 

 areas of the limestone series, known to include Ordovician and Silurian. 



MIDDLE AND UPPER ORDOVICIAN. 



Color, light bluish purple. 



Symbol, 17. 



Distribution: General throughout the continent. In the Arctic mapped with the Silurian (16); 



in the Rocky Mountains of the United States included in narrow bands of Cambrian and 



lower Ordovician (18). 

 Content: Middle to uppermost Ordovician (Chazy to Richmond, inclusive). 



CAMBRIAN AND LOWER ORDOVICIAN. 



Color, purplish red. 



Symbol, 18. 



Distribution: General throughout the continent. 



Content: In general comprises Lower Cambrian (Georgian) to Lower Ordovician (Beekman- 

 town) , inclusive, or so much as may be present. In Appalachian zone, Virginia to Alabama, 

 includes conformable formations below the Olenellus zone; Ocoee ana ChUhowee groups 

 of Safford and other terranes. In the Cordillera, includes Upper Ordovician and Silurian 

 where they are present and bands of color are too narrow for distinct mapping. 



PALEOZOIC, UNDIVIDED. 



Color, light reddish purple. 

 Symbol, 19. 



Distribution: Little-known regions of the northern Cordillera, Montana, and Canada. 

 Content: Paleozoic in general, where data do not suflS.ce to map the divisions separately. Includes 

 some known marine Triassic in the Canadian Rockies. 



METAMORPHIC PALEOZOIC, UNDIVIDED. 



Color, light reddish purple with light dashes. 



Symbol, 20. 



Distribution: Venezuela, Cuba, Santo Domingo, Porto Rico; northeastern Appalachian region; 

 northern Cordillera, California to Alaska. 



Content: Metamorphic sedimentary rocks of known or supposed Paleozoic age, together with 

 possibly pre-Paleozoic schists and some igneous intrusive rocks, which have not been 

 separated. Includes some known marine Triassic in the Canadian Rockies. 



LATE (?) PRE-CAMBRIAN (UNCLASSIFIED, LITTLE ALTERED). 



Color, light brown with blue hachures. 



Symbol, 21. 



Distribution: Northern Canada (Labrador to Northwest Territories excluding the Lake Superior 



region); Avalon Peninsula, Newfoundland; Nova Scotia; Uinta and Wasatch ranges, 



Utah; Needle Mountains, Colorado. 



