234- TJu A^IIK'VtCKll (rcdIlXJ/sf. OctolHT. IHill 
the ieo attrtinod its farthost limits and especially when it was 
rapidly retreating. He thought tliat the view presented first by 
Dana, in his address as retiring president of this Association in 
1855, is more probable, namely, that a great elevation of the 
country, shown l»y fjords and deeph* submerged valleys, at- 
tended and caused the ice accumulation; that the time of de- 
parture of the ice was one of depression, which we now recog- 
nize to be due to the vast pressure of the ice itself; and that 
there has been a partial re-elevation since the Griacial period. 
Neocene and Phistocene contiuint movenicnts. W J McGee. 
Changes in the relative bights of land and sea on the coastal 
plain of the southern Atlantic states during the later part of the 
Tertiary era and in the Pleistocene period are shown by the Ches- 
apeake, Tjafa3'ette ( formerly called Appomattox), and Columbia 
formations. The Chesapeake formation, consisting of fine sands 
and clay, of Pliocene age as know-n by its fossils, w-as deposited 
during a marine su])mergence of the coastal plain and edge of 
the hilly Piedmont belt. After an interval of moderate uplift 
and erosion, the next overljing Lafayette formation, considi-red 
provisionally as Pliocene, was deposited, consisting of gravels, 
sands, and fine loams. These are referred to marine sedimenta- 
tion of the tribute l)rought l)y inflowing rivers from the adjacent 
Piedmont and Appalachian belts, the amount of sul»inergence 
below the present sea level being several hundred feet. No fos- 
sils, however, are found in this formation. Directly following 
the time of the Lafa^'ette deposition, a prolonged stage of high 
land elevation is shown by deep channelling of the Lafayette 
beds, and by great erosion of gorges in the hilly and mountainous 
belts on the west. The next epoch of deposition is the Colum- 
bia, correlated with the earlier glacial epoch, when gravels, sand, 
clay and loam, destitute of fossils and enclosing occasional ice- 
floated Vxjulders, were deposited along the river valleys and over 
considerable areas of the coastal i)lain. This formation is re- 
garded as evidence of estuarine and marine sul)mergence, de- 
creasing from a depth of fully 400 feet in the latitude of New 
York to 150 feet at Washington and perhaps 75 feet in the lati- 
tude of Cape Tlatteras, but thence increasing to about TOO feet 
on the Savannah, again diminishing to less than 50 feet at ^lobile 
bay, and again increasing farther westward and northwestward. 
The Columbia deposition, like the Lafayette, was iuiniediately 
