454 GEOLOGY. 



If similar relations existed during the earlier stages of Quaternary 

 deposition, the seaward edges of the deposits of each principal stage 

 of deposition may be marine. It is probable also Unit the series con- 

 tains estuarine phases of sedimentation, and it can hardly be doubted 

 that each subdivision now recognized on the land has its equivalent 

 (in time) marine phase beneath the sea. 



The essential contemporaneity of the Cape May formation with 

 the last glacial epoch, seems to be indicated by the phenomena of the 

 northern part of the Coastal Plain, and it seems not improbable that 

 the earlier members of the Quaternary system of the coast were con- 

 nected with earlier glacial epochs. 



In recent times, dunes have been developed at numerous points 

 along the coast, and their development and destruction is still in 

 progress. 1 Humus deposits also have somewhat extensive develop- 

 ment in the tidal marshes, and to a less extent elsewhere. 



In the Interior. 



Some of the non-glacial Pleistocene formations of the interior, 

 notably the loess, the valley trains, etc., have been referred to in con- 

 nection with the glacial drift. Apart from such formations, there 

 are others which seem to be measurably or wholly independent of 

 the ice. 



The wide-spread gravels of the western plains, largely of late Ter- 

 tiary age, have been referred to, but the deposition of gravels in this 

 region probably continued into the Pleistocene, is indeed still in progress. 

 In the general absence of fossils, and with the slight measure of study 

 which has been devoted to them, Tertiary and Quaternary gravels 

 have not been sharply differentiated in the interior. The deposits of 

 this class are largely fluviatile. 



In some sandy regions, and along some valleys, there are tracts 

 and belts of dunes for which the semi-arid conditions are favorable. 

 Perhaps the most considerable area of dunes is in central Nebraska, 

 where an area of 24,000 square miles is said to be covered by them. 2 



1 See for example, the Norfolk, Va.-N. C, folio, U. S. Geol. Surv. 



2 Darton, 19th Ann. Rept. U. S. Geol. Surv., Pt. IV; see also topographic maps 

 of Camp Clarke, Browns Creek, and St. Pauls sheets, and the folios of the state, pub- 

 lished by the U. S. Geol. Surv. 



