342 HATCHER — MARINE AND XON-MARINE FORMATIONS. [April 7, 



lying bed belongs to a separate and distinctly more recent age 

 than the underlying deposit. To the present writer this assump- 

 tion appears in not a few instances to be quite unwarranted, the 

 burden of evidence when carefully considered being in favor 

 rather of considering the two formations, largely at least, as con- 

 temporaneous in origin, marine and non-marine conditions having 

 existed simultaneously not over the same but over adjacent regions, 

 each giving origin to its characteristic deposit and the marine ' 

 beds appearing above or below the non-marine according to whether 

 the sea was encroaching upon or receding from the land-mass 

 during the period of their deposition. 



The physical conditions that prevailed during the deposition of 

 any geological formation or series of formations and the manner in 

 which a marine deposit is replaced by a non -marine or vice versa, 

 are best understood by a study of those regions where, under 

 existing conditions, similar deposits are in process of formation. 

 As an illustration let us consider the conditions that at present 

 prevail almost continuously along our Atlantic coast from Florida 

 to Long Island. Throughout this entire coast line a broad and 

 little elevated coastal plain extends inland from the sea to the east- 

 ern foothills of the Appalachian Mountains, while to the eastward 

 of this coast line there lies an equally broad and gently inclined 

 continental plateau at present but little submerged beneath the 

 sea. The eastern limit of this submerged portion of the continen- 

 tal plateau may be regarded as having formed the coast line of the 

 continent at some former period in our earth's history, when the 

 eastern portion of this continent stood at a greater elevation than 

 at present. It was during this earlier period of increased elevation 

 that the Appalachians suffered most from denudation and that the 

 coastal plan, together with the submerged continental plateau, were 

 formed, not as at present differentiated, but as a continuous coastal 

 plain reduced by erosion to a more or less uniform base level 

 extending westward from the eastern limits of the present conti- 

 nental plateau to the foothills of the mountains. A glance at any 

 good map of this region will reveal the fact that the entire coast 

 line, more especially to the northward of Charleston, is deeply 

 indented by numerous shallow sounds and bays, like Delaware and 

 Chesapeake Bays in the north and Albemarle and Pamlico Sounds 

 farther south, while the country for many miles inland from the 

 coast frequently consists largely of more or less impenetrable 



