292 HISTORICAL GEOLOGY 



miles wide), probably at but few places exceeding 25 or 30 feet 

 in thickness, along the northwestern border of the Coastal Plain 

 province. They occur for the most part at elevations of from 200 

 to 500 feet and form mouth-like coverings which cap the tops of, 

 and lap down over the slopes of, the pre-Lafayette hills. The 

 materials consist of sandy loams and sands, as a rule coarse and in 

 places arkosic, and having at their base at many places a bed of 

 coarse gravel and cobbles." 1 In Maryland the Lafayette is quite 

 distinctly terrace-like. According to one view it is of continental 

 origin and was deposited as a result of "a comparatively rapid 

 Pliocene uplift in the Appalachian region" (W. H. Dall), which, 

 early in the Pliocene, had become mantled with deep residual soil 

 so that the revived streams picked up and carried great loads of 

 debris which were spread over the relatively flat lands near sea 

 level. Another explanation is that the Lafayette was of marine 

 origin, due to simultaneous depression of the Coastal Plain district 

 and elevation of the Piedmont Plateau and Appalachian areas 

 when " streams gorged with detritus from the decayed, uplifted 

 Piedmont above rushed down to the sea and poured their contents 

 into the ocean" (G. B. Shattuck). The most likely view is that the 

 Lafayette is a normal marine terrace, much like the later ones 

 below described, and that, "with the successive oscillations of the 

 coast line, terraces have been formed at levels where the sea has 

 stood for any considerable period of time" (W. B. Clark). Careful 

 search has failed to produce any marine fossils from the formation. 



Gulf Coast. — During Eocene-Oligocene time extensive sedi- 

 mentation, both marine and non-marine, took place over the Gulf 

 Coastal Plain area. The Mississippian embayment (see Fig. 180) 

 extended northward (to the mouth of the Ohio River) as it did in 

 the Cretaceous, and the unconformity between the Cretaceous 

 and Eocene clearly shows a transgression of the sea over the area 

 in Eocene time. Marine conditions in this embayment were, 

 however, more or less interrupted as proved by the considerable 

 development of non-marine deposits such as lignite beds. Over 

 Florida, the Gulf Coast of Mexico, and much of the coast of Texas, 

 true marine deposition went on during practically all of Eocene 

 and Oligocene times. 



During Miocene time the Mississippi embayment was greatly 



1 The Coastal Plain of North Carolina: North Carolina Geological and 

 Economic Survey, 1912, p. 359. 



