178 Professor H. D. Rogers, on the Geology and [Feb. 8, 



The Atlantic Plain, or sea-board belt of the Atlantic slope, no- 

 where rises above 100 feet from the ocean level. From Long Island 

 to North Carolina, though intersected by many tidal creeks, it is 

 not marshy, except near the ocean, and bordering the estuaries of 

 the Delaware and Chesapeake ; but farther to the south-west, through 

 North and South Carolina, Georgia, and Florida, its seaward half is 

 excessively swampy and much overflowed. 



Geologically, this ocean border is composed exclusively of 

 cretaceous and tertiary deposits : the former consisting of clays and 

 sands, including thick wide-spread beds of pulverulent green sand, 

 greatly valued as a fertiliser for the soil ; the latter, or tertiary, of 

 sands, clays, and beds of shell marl, with few or no concreted rocky 

 layers. The cretaceous strata outcrop along the continental side of 

 this plain in a narrow zone, extending from the northern sea coast of 

 New Jersey to the Chesapeake, and reappear again low upon some 

 of the rivers of the Carolinas and Georgia ; but, throughout a large 

 part of the plain, they are deeply covered by the tertiaries. The 

 eocene tertiary strata have a narrow long line of outcrop in a cor- 

 responding position along the western edge of the plain, from the 

 Potomac to the Cape Fear River; they reappear again from under 

 the middle tertiary beds, in a more central position in the plain, from 

 the Cape Fear River to the Altamaha. Still farther to the south- 

 west, these eocene beds fringe the southern edge of the cretaceous 

 regions of Georgia, Alabama, and Mississippi, south of the termina- 

 tion of the Appalachian Mountains. This wide southern tract of 

 eocene extends southwards into the interior of the peninsula of 

 Florida, showing this peninsula to have originated as early at least 

 as the morning period of the tertiary day. 



The miocene tertiaries cover nearly the whole of the tide-water 

 plain, except the narrow eocene strip on the west, and a pliocene 

 area on the sea coast of Virginia and North Carolina, from southern 

 New Jersey, through Delaware, Maryland, Virginia, and North 

 Carolina. 



The pliocene deposits skirt, at intervals, the entire Atlantic 

 sea coast from the Chesapeake to Florida, and also the whole 

 coast of the Gulf of Mexico, from Florida to Texas ; forming, for 

 the most part, a fringe to the eocene beds, the miocene not having 

 been deposited in these regions. 



Geological Features of the United States. 



Turning, next, to a more special description of the geological 

 features of the United States, the speaker sketched briefly the great 

 natural areas occupied by its separate formations. 



1st. To the north of the east and west Lawrentine watershed, 

 which itself consists generally of the ancient crystalline rocks, in- 

 cluding the older metamorphic or gneissic, later raetamorphic or 

 azoic, or non-fossiliferous palaeozoic strata, and many plutonic out- 

 bursts ; — there extends to a high latitude, and filling a large part of 



