THE MIOCENE PERIOD. 261 



Oligocene. The fauna of the Chesapeake series has been interpreted to 

 indicate a climate somewhat cooler than that which had preceded, and 

 it has been conjectured that the change was the result of an uplift in 

 the latitude of South Carolina, the axis of the uplift extending seaward 

 sufficiently to divert the Gulf Stream far to the eastward, allowing the 

 cooler waters of the northern coast to affect the coast farther south 

 than before. 1 This suggested explanation hardly seems adequate, and 

 the question may perhaps fairly be raised whether the Miocene fauna 

 of the Southern States does not represent the southward migration of a 

 northern fauna, rather than a notable change of climate. Such a 

 migration might perhaps take place irrespective of climatic change, for 

 the faunas of the north at this time do not appear to indicate any such 

 diversity of climate as now exists. 



The Brandon formation. — Besides the marine Miocene beds along 

 the Atlantic coast, there are, at a few points farther inland, lignitic 

 beds which have been thought to belong to the Miocene. They appear 

 to represent accumulations of vegetal matter in marshes more or less 

 distant from the coast. The beds here referred to have been found in 

 Vermont, Pennsylvania, and Georgia, and have been described under 

 the name of the Brandon formation. 2 With them are sometimes asso- 

 ciated beds of iron ore. The correlation of these various lignitic and 

 ferruginous beds with one another, and their reference to the Miocene, 

 cannot be regarded as beyond question. 3 



The Gulf coast. — The Miocene of the Gulf coast sustains the same 

 general relations to older formations as that of the Atlantic, except 

 that it is not known to be so generally unconformable on the beds 

 below. Excluding the beds classed as Oligocene, the system has but 

 slight thickness. In Florida, the limestone of the series has locally 

 been changed to lime phosphate. 4 The alteration appears to have been 

 effected through organic matter, especially the animal excrements accu- 

 mulated about bird, seal, and perhaps other rookeries. The organic 

 matter furnished the phosphoric acid, which, carried down in solution, 

 changed the carbonate of lime to phosphate. The phosphate has been 

 extensively used as a fertilizer for soils. Similar phosphate deposits 

 are found in other places and in other formations. 



1 Dall and Harris, op. cit. 



2 Rept. of the State Geol. of Vt., 1903-4; and Clark, Bull. 83, U. S. Geol. Surv. 

 Dana assigns the Brandon formation to the Eocene, Manual of Geology, 4th ed. 



3 Perkins, Bull. Geol. Soc. Am., Vol. XVI. 



4 Fenrose, Bull. 46, U. S. Geol. Lurv. 



