GEOLOGIC DIVISIONS MAPPED. 9 



in the map of North America, wherever the differences of knowledge are of such a 

 degree as to occasion material difficulties in applying a uniform classification. The 

 instances are readily recognized by the arbitrary boundary which separates several 

 formations or series from a comprehensive major class that comprises them all. 

 Each such occxu"rence points to an opportunity for investigation. 

 The legend of the map in detail is as follows : 



Qt'ATERNARY. 



Color, cream. 



Symbol, 1. 



Distribution: Shown only where the Quaternary completely conceals the underlying formations. 



Content: Alluvial, lacustrine, and desert-basin deposits, glacial drift (in small part only), and 

 beach, dune, and marine deposits of the Atlantic and Gulf coasts; all comprised in one cate- 

 gory (Quaternary) and shown by the one color and pattern. 



PLIOCENE. 



Color, lemon-yeUow. 



Symbol, 2. 



Distrib-ution: The Pliocene is distinguished on the Atlantic and Gulf coasts, so far as surveys per- 

 mit, in Cahfornia, and in northern Nevada. Elsewhere on the map it is classed with the 

 Quaternary (1), as in the valley deposits of the Great Basin; or with the Miocene under the 

 heading "Ijater Tertiary" (4). The Lafayette formation of the Atlantic and Gulf slopes, 

 including the Altamaha of Georgia, is shown only where it completely conceals the underly- 

 ing formations. 



Content: Marine Pliocene of the Coast Ranges of California; Plumboldt formation (nonmarine) 

 of Nevada; marine Pliocene and Lafayette of the Atlantic and GuK slopes east of the Mis- 

 sissippi, including Altamaha of Georgia ; also Yucatan. 



MIOCENE. 



Color, light yellow. 



Symbol, 3. 



Distribution: The Miocene is separately indicated on the Pacific coast and on the Atlantic and 



Gulf coasts, so far as surveys permit. Elsewhere on the map it is comprised with Pliocene 



under the term "Later Tertiary" (4). 

 Content: Monterey shale and equivalents of the Pacific coast; beds of Carrizo Creek, Cahfornia; 



and mai-ine Miocene of the Atlantic and Gulf coasts. Does not include so-called "Arctic 



Miocene" nor "Old Miocene, " both of which are included in the "Marine Eocene." 



LATER TERTIARY (mIOCENE AND PLIOCENE). 



Color, yellow. 



Symbol, 4. 



Distribution: Mapped where Miocene or PHocene are recognized but can not be separated or be 

 individually identified in the present state of knowledge. 



Content: Pacific coast marine deposits ; Alaskan Arctic coastal plain deposits ; fluviatile and lacus- 

 trine beds of the Interior; western Gulf coast marine formations; and late marine Tertiary 

 of Mexico, Central America, and South America. 



MARINE OLIGOCENE. 



Color, Ught orange (ruling). 



Symhol, 5d. 



Distribution: Atlantic and Gulf coasts of the United States, where it is separated from the 



Eocene. Elsewhere combined with the Eocene as "Earlier Tertiary. " 

 Content: Marine Oligocene of the Atlantic and Gulf slopes. 



