CHAMPLAIN EPOCH. 557 



Both the elevation of the previous epoch and the subsidence of this 

 seem to have been greater along the axis of the continent, the valley of 

 the Mississippi, than on the coasts. Hilgard finds evidence in the 

 Orange sand-deposit, and in the thickness of the subsequent Champlain 

 deposit, of an elevation of 450 feet above the present level, and a depres- 

 sion of 450 feet (for this is the maximum elevation of the Champlain 

 deposit above the same level), or an oscillation of 900 feet in Louisiana. 

 The submarine channel of the Mississippi, recently found beyond the 

 limits of the delta deposit, show an even much higher elevation in the 

 Gulf region (Spencer). Farther north it is probably still greater. 



3. River Terraces and Old Flood-Plain Deposits. — Nearly all the 

 rivers in the eastern portion of the continent, over the Drift region, are 

 bordered with high terraces, which have been cut wholly out of an old 

 flood-plain deposit belonging to the Champlain epoch. In fact, these 

 rivers show first an elevation, then a depression, and finally a partial re- 

 elevation ; in other words, all the oscillations of the Quaternary period 

 are recorded by them. 



An examination of the rivers north of the fortieth parallel shows : 

 1. An old river-bed far deeper and broader than the present ; 2. This 

 deep and broad river-bed is filled up, often several hundred feet deep, 

 by old river-deposit ; 3. Into this old river-deposit the shrunken stream 

 is again cutting, but is still far above the bottom of the old river-bed. 

 This cutting into the old river-deposit produces bluffs and terraces on 

 each side. It is evident that the great river-bed was gouged out during 

 late Tertiary and early Glacial epochs ; the filling up took place during 

 the Champlain, and the cutting and terracing during the Terrace 

 epoch. Some of these old river-channels, as, for example, that of the 

 St. Lawrence, the Hudson, and the Delaware, may be traced far out to 

 sea, to the sunken borders of the glacial continent. 



Fig. 932 is an ideal section across a river-bed in the Drift region, 

 in which b b is the old river-bed, scooped out during the epoch of ele- 



Fig. 932.— Ideal Section across a River-bed in Drift Region: bbb, old river-bed; R, the present 

 river; 1 1, upper or older terraces; V V ', lower terraces. 



vation ; the dotted line represents the highest level to which the old 

 river-deposit accumulated, and the shaded portion that part of such 

 deposit which still remains. The upper terraces, t t, are of course the 

 oldest, the lower ones being made as the shrunken stream cut deeper 

 and deeper. 



