24 



INDEX TO THE STRATIGEAPHY OF NOETH AMERICA. 



Some familiar usages are those of red, the color of fire, for igneous rocks; pink 

 for the ancient crystalline rocks; blue, the color of the rock, for limestone; yellow, 

 by similar association, for sandstone; and many others in which the suggestion of 

 the color has a mnemonic value. » 



Another class of usages comprises those established officially by the practice 

 of a government survey or by agreement among such surveys. Among those which 

 have been developed to meet a general application and which are therefore most 

 comprehensive in character, there are two that have been considered for the map 

 of North America — the color scheme adopted by the International Geological 

 Congress for the general map of Europe, and that designed by the United States 

 Geological Survey for the Geologic Atlas of the United States. The following 

 table shows their resemblances and differences: 



Colors and color schemes. 



Natural order of tints, hues, and 

 shades. 



Yellow., orange-tinted (cream). 



Yellow, light 



Yellow, medium 



Yellow, dark 



Yellow, greenish 



Citrine, yellowish brown 



Citrine, medium brown 



Citrine, greenish brown 



Green, yellowish 



Green, light 



Green, medium 



Green, dark 



Green, bluish 



Olive, greenish 



Olive, medium 



Olive, bluish 



Blue, greenish 



Blue, gray 



Blue, light 



Blue, medium 



Blue, dark 



Blue, purplish 



Purple, bluish 



Purple, light 



Purple, medium . . 



Purple, dark 



Purple, reddish- .. 

 Russet, purplish. . 



Russet 



Russet, reddish — 



Red, russet 



Red, light 



Red, medium 



Red, dark 



Red, yellowish 



Orange, reddish. . . 

 Orange, medium. . 



Orange, light 



Orange, yellowish. 



International Euro- 

 pean color scheme. 



Quaternary . 



Pliocene 



Miocene 



Oligocene. . 



Permian. 



Eocene 



Cretaceous, Upper. 

 Cretaceous, Lower. 



Wealden 



Volgian 



Cambrian (dark) . . . 

 Devonian (dark). . . 



Silurian (dark) . 



Carboniferous (dark) 



Jurassic, Upper... 

 Jurassic, Middle. 



Jurassic, Lower. 

 Triassic 



Gneiss and protogine 



Eruptives. 

 Schists 



Eruptives. 

 Effusives . 

 Effusives. 

 Effusives. 



United States Geological Survey. 



Geologic Atlas of the United 

 States. 



Pliocene and Miocene . . 

 Eocene and Oligocene. 

 Cretaceous, upper part. 



Cretaceous 



Cretaceous, lower part. . 

 Jurassic 



Archean. 



Triassic . 



Carboniferous 



Carboniferous, upper part. 

 Carboniferous, lower part. , 



Devonian. 



Silurian 



Ordovician (reddish). 

 Algonkian 



Cambrian . 



Geologic map of North 

 America. 



Quaternary. 



Miocene. 



Pliocene. 



Cretaceous, late Upper. 

 Cretaceous, Upper. 

 Cretaceous, Lower. 

 Triassic. 



/Jurassic (light). 

 \Triassic and Jurassic (dark). 

 /Permian (light). 

 \Pennsylvanian (dark). 



Carboniferous. 



Mississippian. 



Devonian. 



Ordovician, middle and upper. 



Silurian. 



Paleozoic. 



Eruptives. 



Cambrian and lower Ordovician. 



Late pre-Cambrian. 

 Earlier pre-Cambrian. 



Pre-Cambrian. 



Eruptives. 



Effusives. 



Eocene. 



Oligocene. 



