98 J. D. Dcmctr— -Flood „f 'tin < '» 



Art. XIII— On the Flood of the Connertict Rn-er Valley /,-.,, 



the mdtiii'j of the Quaternary Glacier ; by JAMES D. Dana. 



[Concluded from p. 3t3, volume xxiii.] 



6. The question as to the Elevation of the Land. 



The remaining question in connection with the discussion 

 ivsj-.ect.inii' the Connecticut Valley during the era of the great 

 flood is that relating to its apparent depression at the time: 

 —Whether the change in pitch, which was proved to have been 

 a fact, was due to a change in land-level, or only to a change 

 in sea- lev el. 



To understand the events of the Glacial era and that follow- 

 ing and reason correctly on the facts, we should know which 

 of these views is right, and, in order to know, take evidence 

 from the region. 



Toward this end, we may first compare the requirements of 

 an hypothesis which refers the change to a change in sea-level 

 with the facts observed. If the facts do not accord with the 

 demands of such an hypothesis, we are then free to adopt the 

 other view — that the depression of the land was actual and 

 not merely apparent. 



It should be understood, in advance, as a fact in terrestrial 

 physics, that any rise in the ocean's level increasing northward 

 produced by a change in the position of the earth's center of 

 gravity would be,* effectively, a change (1) in the height of 

 the land ; and (2) a change in the pitch of its surface ; and, 

 New England, like the rest of the globe, being within the area 

 so affected, it would be a change in pitch for the Connecticut 

 Yalley and the region around, as well as for the coast region. 

 For, the ocean's surface is the reference-plane of horizontality as 

 well as elevation, and the attraction determining its level would 

 affect not o imente used 



over it for obtaining horizontal or perpendicular lines. 



Only one source of a change in the position of the earth's 

 center of gravity has been suggested in this connection— that 

 from the forming of a polar ice cap of great thickness, during 

 a glacial era in one hemisphere or the other, as in the hypoth- 

 esis of Adhemar, adopted by Croll and others, this cause lead- 

 ing to an increased pole-ward accumulation of the oceanic 

 waters in the ice-covered hemisphere. 



The following are among the facts bearing on this subject. 



(1.) There is no correspondence between the amounts of 



change deduced from observations and those required by the 



* Assuming that the earth is so far rigid that it would not suffer deformation— 

 or a depress;.- -. gurfaoe. 



