466 W. J. Mo Gee — Formations of the Atlantic Slope. 



The vicissitudes recorded in the Columbia formation and 

 associated phenomena may be graphically represented as in the 

 accompanying diagrams. It should be pointed out that the 

 earlier part of the record is shadowy, that the quantitative esti- 

 mates are but roughly approximate, and that the later part of 

 the record is obscured by the fall-line displacement (which can- 

 not be here discussed) ; yet the graphic interpretation of the 



TERTIAF 



Y 



QUATERNARY 







PRE- 



IV 



INTER -GLACIAL 



2".°t 3"" 



POST 



GLACIAL 



Degrasja 



on : \ 



Degrada+i on 



: 2 



Degradation 3 



ALTITUDE CURVE 



TEMPERATU 



Imposition of Columbia Formation. 2 Deposition of Trenton Gravels and Champlain ClayS. 3 Accelerated Degradation duett, Human Activities 



later episodes (fig. 2) is reliable qualitatively, though the rela- 

 tions between these episodes and the more important antece- 

 dent vicissitudes is only represented provisionally (fig. 3). 



3. 



TERTIARY QUATER NARY 



BASE -LEVEL PERIOD PER IOD OF PIEDMONT- APPALACHIAN G ORGE CUTTING 1234 



-"*" - TEMfERATURE __CURyg. 



ALTI.TUD.E_.cy.RVE. — 



it 



1 P.'Glacial Period 2 Inter-glacial Period 3 2V and 3".°Glacial Periods 4 Pusi-Glacial Period 



There is a break in geologic history, as commonly inter- 

 preted, between the Tertiary and the Quaternary — a hiatus 

 partly natural and partly taxonomic, and exceedingly difficult 

 to close by reason of diverse methods of classification as well 

 as by reason of the dearth of common phenomena. But the 

 formation under consideration is a superficial deposit of known 

 genesis, intimately connected . with the other Quaternary de- 

 posits of the country ; it is at the same time a f ossiliferous 

 sedimentary deposit as intimately connected with the Tertiary 

 formations of the middle Atlantic slope as these are connected 

 among themselves ; and thus the formation not only covers the 

 natural discontinuity between the Tertiary and Quaternary, but, 

 since it is susceptible of classification with either, closes the 

 taxonomic hiatus as well. So the Columbia formation not only 

 enlarges current conceptions of Quaternary time, and opens a 

 hitherto sealed chapter in geology, but at the same time bridges 

 an important break in geologic history. 



