604 THE PLIOCENE PERIOD 



the phenomena, and abandoned as untenable even where conditions 

 seem most to favor it. The objections to it are (i) the absence of 

 marine fossils; (2) the presence of structural features not indicative of 

 typical marine deposits; (3) the chemical condition of the formation, 

 particularly the high and very unequal oxidation and the meager 

 hydra tion; (4) the topographic relations of the formation, especially 

 the lack of any approach to horizontality in its upper limit; and (5) 

 the absence of shore phenomena. 



Marine Formations 



The Atlantic coast. If fossils be the test, Pliocene beds of 

 marine origin have little development on the eastern side of the 

 continent. In Florida only (Caloosahatchie beds) have beds con- 

 taining marine fossils any considerable extent at the surface, though 

 small patches are known farther north. They may be parts of a 

 continuous formation, chiefly concealed. The time relations of 

 these marine Pliocene beds to the Lafayette are undetermined. 

 Pliocene beds of marine origin have not been identified certainly 

 between Florida and Texas, but they cover considerable areas farther 

 south, as in Yucatan. 



The Pacific coast. 1 Marine sedimentation along this coast was 

 confined to narrow limits (Fig. 502). The deposits are chiefly 

 clastic. Their maximum known thickness is found south of San 

 Francisco, where about 4,000 feet of strata (Merced series) are 

 exposed. 2 The non-marine part of the system (Paso Robles forma- 

 tion) is as thick in the San Joaquin valley. 



Crustal Movements 3 



The tendency to crustal movements, both warping and faulting, 

 which had characterized the western part of the continent since 

 the close of the Mesozoic, seems to have continued at least inter- 

 mittently through the Pliocene. Perhaps these movements were 

 in many places no more than continuations of those begun earlier. 



About the close of the period, movements were extensive and 



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



2 Lawson, Science, Vol. XV, 1902, p. 410, and Hershey, Am. Geol., XXIX, 

 p. 359, give the Pliocene of California greater thicknesses. 



3 LeConte, Am. Jour. Sci., Vol. XXXII, p. 167, 1886, Bull. Geol. Soc. Am., 

 Vol. II, p. 329, Jour. Geol., Vol. VII, p. 546, 1899; Hershey, Science, Vol. Ill, 

 p. 620, 1896, and Button, Mono. I, U. S. Geol. Surv. 



