THE MIOCENE PERIOD 807 



thickness of 700 feet, in Maryland, 1 about 400 feet, and in North 

 Carolina it is still thinner. 



The Miocene of the Atlantic coast is generally called the Chesa- 

 peake formation. This was formerly regarded as Upper Miocene, 

 the former Lower Miocene being now classed as Oligocene. The 

 fauna of the Chesapeake series has been interpreted to indicate a 

 climate somewhat cooler than that which had preceded. 



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 

 Miocene of this region has but slight thickness. In Florida, the 

 Miocene limestone has been changed locally to lime phosphate. 2 

 The alteration appears to have been effected through organic matter, 

 especially the animal excrements accumulated 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 the phosphate. The phosphate has been ex- 

 tensively used as a fertilizer for soils. The Miocene is represented 

 in Alabama and adjacent stages (the Pascagoula formation) and in 

 Texas (Oakville beds), where both marine and non-marine phases 

 are present. Much of the oil of Texas and Louisiana (Beaumont, 

 Sour Lake, Saratoga, Jennings, etc.) comes from dolomized lime- 

 stone which overlies Eocene (or Oligocene) clays, and is probably 

 Miocene. 3 



The Pacific coast. 4 At the beginning of the period, the sea 



encroached upon the Pacific coast, covering considerable areas 



which were land during the Oligocene time. It flooded the southern 



part of the central valley of California early in the period, and 



later the northern part as well. At about the beginning of the 



I period, faulting seems to have affected considerable parts of Cali- 



jfornia, and some of the planes of movement at that time have 



I served as planes of movement until now. This was the time of 



1 Clark, Maryland Geol. Surv., Vol. I, and volume on the Miocene, 1904. 



2 Penrose, Bull. 46, U. S. Geol. Surv. 



3 Hayes, Bull. 213, U. S. Geol. Surv., p. 346. 



4 Arnold, Ralph, Jour. Geol., Vol. XVII. 



