CHAPTER XXVIII 

 THE MIOCENE PERIOD 1 



The distribution of the Miocene system (Fig. 541) shows that 

 the geography of the North American continent was much the 

 same during the Miocene period as during the Eocene, the sea 

 covering no more than narrow borders of the present land. The 

 slight emergence of the coastal borders after the Eocene (or early 

 Oligocene) was followed by a slight submergence of the same regions 

 during the Miocene. In the western interior, wide-spread terres- 

 trial aggradation of all phases continued, but the sites of principal 

 deposition differed somewhat from those of the preceding 

 period. 



The Atlantic coast. In its surface distribution, the Miocene 

 sustains the same relation to the Eocene that the latter does to 

 the Cretaceous, though it sometimes overlaps the Eocene, com- 

 pletely concealing it. There is generally a slight unconformity be- 

 tween the Miocene and the Eocene (or Oligocene). Like the other 

 formations of the Coastal Plain, the Miocene beds dip seaward and 

 are concealed by younger beds some distance to landward from the 

 present shore line. The general relations are indicated by Fig. 499. 

 The system originally extended inland far beyond its present border, 

 as shown by numerous outliers. 



The Miocene of the Atlantic coast is composed chiefly of un- 

 consolidated sand, clay, and shell marl. In places, diatomaceous 

 earths are found in beds of such thickness (30 or 40 feet) as to be 

 valuable commercially. In New Jersey, 2 the Miocene reaches a 



1 For general summary of literature on the Miocene (Miocene and Plio- 

 cene) 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 Reports of the State Geologist of New Jersey, especially Report of 1892. 



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