CHAPTER XVII. 



THE MIOCENE PERIOD. 1 



The distribution of the Miocene beds (see map, Fig. 442) shows that 

 the geography of the North American continent during the Miocene 

 period was much the same as during the Eocene. The slight emergence 

 of the Atlantic and Gulf coastal belts after the Eocene (or early Oligo- 

 cene) was followed by a slight submergence of the same regions during 

 the Miocene. Locally, and perhaps generally, along the Atlantic coast, 

 the Miocene submergence exceeded the Eocene. The Mississippi em- 

 bayment of the Miocene was less extensive than that of the Eocene, 

 having been constricted by the partial filling or emergence of the lower 

 Mississippi basin. A portion of northern Florida, elevated after the 

 Eocene (or Oligocene, p. 215), constituted an island. On the Pacific 

 coast, the shore line was shifted westward somewhat beyond its present 

 position before the beginning of the Miocene, but as the period advanced, 

 the sea again encroached upon the land, finally reaching the foot of the 

 Sierras. At no time during the period, so far as known, did the sea 

 cover more than narrow borders of the present North American conti- 

 nent. The crustal movements which preceded the Miocene seem to 

 have closed such connection as there was between the Altantic and 

 the Pacific across Central America or the Isthmian region during the 

 Eocene. 2 In the western interior, wide-spread terrestrial aggradation 

 of all phases continued, but the sites of principal deposition differed 

 somewhat from those of the preceding period. 



The Atlantic coast. — The Miocene beds of the Atlantic coast are 

 general^ unconformable on the Eocene (or Oligocene), but it does not 



1 For general summary of literature on the Neocene (Miocene and Pliocene) prior 

 to 1892, see Dall and Harris, Bull. 84, U. S. Geol. Surv. The bibliography up to 

 1896 is found in the 18th Ann. Rept. U. S. Geol. Surv., Pt. II (Dall). 



2 Hill, The Geological History of the Isthmus of Panama and Portions of Costa 

 Rica. Reviewed in Jour, of Geol., Vol. VI, p. 661. 



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