and Deposits of Flooded Rivers. 47 



along the rivers, and prevailingly finer gravels, sand, clay and 

 silt between the rivers, seem to me referable to fluvial action, 

 dependent on the conditions already noted, without submerg- 

 ence by the sea, during times of great Quaternary elevation of 

 the continent, while its northern part was becoming covered 

 with the ice-sheets of the first and second G-lacial epochs. The 

 lack of fossils accords better with such deposition by flooded 

 rivers ; and, in harmony with this view, the stratigraphic rela- 

 tions indicate for the Appomattox an early Quaternary age, 

 and for the Columbia a much later age, yet antedating that of 

 the terminal moraines and stratified valley drift of the adjacent 

 glaciated area of Pennsylvania, JSTew Jersey, and Long Island, 

 which belong to the culmination, and in larger part to the 

 stages of recession, of the later ice-sheet.* 



In the lower Mississippi basin, the great uplift introducing 

 the earlier glaciation seems to have been marked by so exces- 

 sive precipitation and heavy river-floods that thick deposits of 

 sand and gravel, constituting the principal mass of the " Orange 

 Sand," were filled into the channel which had been cut by the 

 river in the Tertiary beds of its lower course while it was above 

 the sea level, but had only a moderate elevation, during the 

 greater part of the Pliocene period. About the time of the 

 maximum extension of the ice-sheet of the first Glacial epoch, 

 this basin was depressed to approximately the height which it 

 now has, but with less descent in its slope seaward, as shown 

 by the loess. On account of the diminished transporting 

 power of its floods, deposition along the lower valley ceased 

 for a time, and the " Orange Sand " was partially eroded, until 

 at length the floods and silt supplied by the melting of the ice- 

 sheet filled the newly formed channel, and overspread the 

 gravel and sand areas, depositing the Port Hudson beds and 

 loess. During the long interglacial epoch these beds, with 

 the " Orange Sand," were immensely eroded, and more espe- 

 cially at the time of northward elevation initiating the second 

 Glacial epoch. Again, from the melting of the later ice-sheet, 

 vast floods, bringing some gravel and sand, but more fine silt 

 or loess, poured down this valley, spreading their deposits 

 along the bottom of the interglacial channel in a flood-plain 

 200 to 300 feet below the uplands and sixty miles wide from 

 Cairo southward ; and, at a diminished rate, the deposition of 

 the river silt over this bottom-land is still going on at every 

 flood stage, f 



* This Journal, III. vol. xxxv, Feb., and April to June, 1888: vol. xl, pp. 15- 

 41, July, 1890; and vol. xl, pp. 237-8, Sept., 1890. 



f E. W. Hilgard, this Journal, IL vol. xlii, May, 1866; vol. xlvii, Jan., 1869; 

 vol. xlviii, Nov., 1869; III, vol. ii, Dec., 1871. T. C. Chamberlin. Bulletin Geol. 

 Soc. of America, vol. i, 1890, pp. 469-480. 



