CENOZOIC TIIVIE — TERTIARY. 891 



The epochs of the marine Miocene, as defined from the formations of the Atlantic and 

 Gulf borders, are as follows : — 



1. Chattahoochee : so named by Langdon, from typical exposures on Chattahoochee 

 River, southwest Georgia, and northwest Florida. Dall correlates with the Chattahoochee 

 deposits the Hawthorn beds of central Florida, consisting of phosphatic oolyte, ferruginous 

 gravel, and green clays, the Orthaulax bed and Tampa limestone at Tampa, the Altamaha 

 grits of Georgia, and also the "typical Grand Gulf'' of southern Alabama. The last- 

 named deposits are placed at this horizon because they are "analogous to and probably 

 synchronous " with the Altamaha grits of Georgia, and are overlaid at Roberts, Escambia 

 County, Fla. (according to Smith), by a bed containing Chipola fossils, as identified by 

 Dall. The Chattahoochee fauna is closely related to the Miocene of West Indies, Jamaica, 

 Trinidad, Haiti, Curagoa, Panama, and Costa Rica (Dall). 



2. Chipola : distinguished by Burns, and first named by him in manuscript as the 

 Chipola formation from typical exposures on a river by that name in northwestern 

 Florida. The lower member of the group, the Chipola sands, is famous for its vast 

 number of fossil shells, nearly 400 species having been found at the type locality. This 

 remarkable faunal development is to the Miocene what the Claiborne fauna is to the 

 Eocene ; both occur in slightly ferruginous sands about 16' thick, both appear to be very 

 limited in areal extent, and both occur medially in their respective periods. 



The fauna of the Alum Bluff sands (Dall) immediately overlying the fossiliferous 

 Chipola bed has not been carefully studied. 



All these older Miocene deposits are characterized by a warm-water or subtropical 

 fauna (Dall). 



3. YoRKTOVvN : named from Yorktown, Va., by Dana (1863). It is the time-equiva- 

 lent of the Chesapeake group of Darton and Dall (1891). It includes the Miocene of the 

 Atlantic slope as known to geologists prior to 1887. The section at Alum Bluff shows 

 that this group lies above the Chipola. It is well developed in Duplin County, N. C, at 

 Yorktown, and elsewhere in Virginia, and along the river courses in Maryland. Calvert 

 Cliffs on the west shore of Chesapeake Bay exhibit three well-defined fossiliferous zones, 

 named, in descending order, the St. Mary's, Jones Wharf, and Plum Point. Beds lower 

 still in the series are found on the eastern shore of Maryland, and with these in New Jersey 

 Dall finds traces of older Miocene fossils. It has been identified by its fossils on Martha's 

 Vineyard by Dall. 



A modification of this faiina is found in the Galveston Deep Well, Tex., between 

 depths of 2000' and 3000'. 



Since the publication of Gabb's work on the California Geological Survey the 

 Miocene as well as Pliocene fossil remains of the Pacific slope have received little attention. 

 As a rule the Miocene fossils are poorly preserved, and are often embedded in firm 

 rock. Their general aspect indicates a horizon more nearly that of the Yorktown group 

 than that of the older Miocene. 



In Georgia and Florida, where newest Eocene and oldest Miocene occur, there is 

 a marked faunal break between the two, yet there are several species in common. In 

 Maryland and Virginia, where Yorktown Miocene rests upon Lignitic Eocene, the break 

 is complete, not one species being found common to the two. The upper, or Yorktown, 

 Miocene was characterized by a fauna indicative of a temperature similar to that of to-day. 



The Ashley marl bed of South Carolina, containing phosphatic nodules with fossils 

 in them, which was referred by Tuomey doubtingly to the Eocene, affords Miocene 

 fossils (1894). Of marine Pliocene, there are the Floridian deposits of Heilprin as modi- 

 fied by Dall (1892); t\i& Pliocene of Tuomey (1848), excluding some Miocene beds as 

 determined by the investigations of C. W. Johnson and Dall. To this period have been 

 referred the Orange sand group of Safford (1856), occurring in Tennessee, the Orange 

 sand of Hilgard (1860), in Mississippi and Tennessee, the Orange sand, or Lagrange 



