LATER TERTIARY (MIOCENE AND PLIOCENE). 813 



"In structural composition the formation is a unit, varying from place to place in local 

 characters yet indivisible throughout its area of 250,000 square nules, save on arbitrary grounds." 



The formation is important especially in the interstream areas across South Carolina, 

 northern Florida, and each State from Georgia to southern Ilhnois. 



PLEISTOCENE. 



Marine Pleistocene deposits cover considerable areas along the coasts of South Carolina 

 and Georgia and are greatly developed in Florida, where Pleistocene marls, coquina beds, and 

 limestones underlie over half the present land surface of the State."^ 



Below the Lafayette level in the south Atlantic and GuK Coastal Plain States are several 

 persistent terraces above the present flood plain, representing McGee's Columbia group. From 

 Georgia to Tennessee there are at least two — (a) one major terrace between the Lafayette and the 

 "second bottoms" and (&) the "second bottoms." The loess of the Mississippi seems correlative 

 with the major terrace below the Lafayette level. The terraces slope coastward and merge 

 with shaUow-water and estuarine deposits, to which in Louisiana HUgard has applied the 

 name Port Hudson group. 



H-J 13-14. GREAT PLAINS, COLORADO, KANSAS, OKLAHOMA, NEW MEXICO, AND TEXAS. 



Darton ^^*° maps the Miocene (Ogalalla and Arikaree formations) southward 

 from Nebraska (see p. 822) through Colorado and Kansas into Oklahoma, Texas, 

 and New Mexico. The following notes are taken from a paper by Gould i^"" 



Lying unconformably upon the surface of the red beds and Cretaceous over a large part of 

 western Oklahoma is an extensive deposit of Tertiary rocks, the exact age of which has never 

 been determined with accuracy. Paleontological evidence is rare, but, following the usual 

 classification of beds of apparently the same age in western Kansas and Nebraska, there seems 

 no vahd reason for not considering them Miocene or PUocene. * * * 



With the exceptions of the alluvium and sand hiUs the Tertiary is the uppermost forma- 

 tion in Oklahoma. The red beds underlie it, except that between the red beds and the Tertiary 

 occur sometimes Comanche Cretaceous members. * * * 



In general the later Tertiary occupies the uplands of the western half of Oklahoma, almost 

 always occurring on the high divides between the streams. * * * 



The Tertiary consists for the most part of clay, sand, and gravel. These materials are in 

 no regular stratigraphic succession. * * * In places the entire thickness of the formation 

 is clay; again sand and gravel predominate, and often deposits of different character wUl be 

 interbedded. * * * 



The clay is usually white or pinkish and sometimes forms steep banks or cliffs along the 

 bluffs or around the heads of canyons. To the harder ledges the name "mortar beds" has 

 been applied. * * * 



The sand is of various degrees of fineness and is composed for the most part of quartz, 

 although other minerals are present. The grains, when examined under the microscope, are 

 usually rounded. * * * 



"Tertiary pebbles" is the term usually applied by geologists to the smooth, rounded, 

 waterworn pebbles scattered abundantly over the slopes and points throughout western Okla- 

 homa and Kansas. These pebbles have been washed out of the Tertiary deposits, of which 

 they often constitute a moderately large proportion. They are frequently cemented together and 

 form a hard conglomerate rock known as Tertiary grit, which on exposure forms conspicuous 

 ledges. * * * 



3 For detailed information see papers on Florida by Sanford *'^ and \'auglian.*^5 



