224 The American Geologist. October, i89-^ 
deposited while this low plain was covered by the sea, but the 
Appalachian mountain belt appears to have then stood somewhat 
above its present hight. Between the coastal submergences to 
which the Lafayette and Columbia beds are referred, this plain 
was elevated higher than now and the ('hesapeake and Delaware 
bays were formed by the erosion of the Suscjuehanna and Dela- 
ware rivers. If time since the recession of the latest ice-sheet 
has been 7,000 years, as is shown to be probable by the studies 
of N. H. Winchell, Gilbert, Wright, and others, the amount of 
erosion since the Columbia and Lafayette epochs indicates that 
they were respectivel}' some 200,000 years and 10,000,000 years 
ago, the Lafayette being apparently fifty times as long ago as the 
Columbia, and the latter thirty times older than the last glacial 
epoch. 
In discussion, Mr. Upham (questioned whether a simpler view 
of the epeirogenic movements producing the Lafayette formation 
might not be found in ascribing these beds to deposition by flooded 
rivers descending from the Appalachian mountain region and 
from the Mississippi basin, as shown b}' Hilgard, spreading the 
gravel, sand and loam over the coastal plain during the eai'ly 
part of a time of continental elevation. As this elevation in- 
creased, the rivers would attain steeper slopes and finall}' erode 
much of the deposits which they had previously made. During 
the culmination of the uplift, Chesapeake and Delaware bays 
were excavated, and erosion was in progress at a far more rapid 
rate than with the present low altitude of this region. The time 
ratios assigned to the Lafayette and Columbia formations in com- 
parison with the last glacial epoch may therefore be greatlj' ex- 
aggerated, and they may belong wholly to the Pleistocene or 
Glacial period. 
Prof. E. D. Cope doubted that the physical characters of 
the Lafayette beds could be produced by fluvial sedimenta- 
tion. 
Pres. T. C. Chamberlin considered the question whether the 
Lafayette formation was mainly of marine or of fluvial origin 
undecided, but in New Jersey, at least, according to the studies 
of Prof. Salisbury, the latter view appears the more prob- 
able. 
